The episode picks up right where the previous one left off, as Ash plans to capture a Caterpie in Viridian Forest. He immediately tosses a Template:Ball at the wild Pokémon, and the device pulls Caterpie inside. The Ball hits the ground and begins to shake. Ash, Misty and Pikachu watch as Caterpie tries to break out.
After a few tense moments, the Poké Ball stops shaking, signifying that Ash caught Caterpie. His excitement takes control as he celebrates catching his first Pokémon, holding the Poké Ball and running in circles with Misty, making Pikachu dizzy. When Ash holds the Poké Ball to Misty’s face, she reveals that she has a fear of Bug-types, even if they are contained in a Poké Ball. However, Pikachu is happy to have Caterpie along, and Ash decides to bring Caterpie out, scaring Misty away.
As Caterpie appears, Misty scampers behind a tree. Ash asks Caterpie to crawl up onto his shoulder, but when Caterpie spots Misty, he immediately bolts over to Misty and rubs up on her leg despite her personal discomfort. Misty’s comments about Caterpie being a “disgusting bug” hurt the Pokémon. Misty wants to befriend Pikachu instead, which somewhat irritates Ash as Pikachu is warming up to Misty more quickly than to Ash.
Misty continues to complain about Caterpie and to put “one of the three most disgusting things” back into the Poké Ball. When Ash asks about the others, Misty remarks “Carrots, Peppers, and bugs.” Ash, however, is offended at how Misty’s discomforts are used to hurt Caterpie’s feelings. Ash reassures Caterpie and gets him to climb onto his shoulder. Ash decides to go on without Misty, prompting Pikachu to tag along.
Moments later, Pikachu notices Misty trying to keep up with Ash. Although Misty tries to hide, Ash spots her and asks why she is still following him. Misty brings up the bike he destroyed earlier, and they continue to argue, upsetting Pikachu.
Later that night, Ash sets up for the night near a tree stump, starting a fire. Tucked into his sleeping bag, Ash prepares to retire for the night, while Pikachu and Caterpie sit on the stump. Misty, also set up on the other end of the stump, exchanges a few smart remarks with Ash before both go to sleep, upsetting Pikachu and Caterpie. While the humans sleep, Pikachu and Caterpie enjoy the starlight view and connect with each other. Caterpie looks up to the moon and envisions his desire to fly as a fully evolvedButterfree.
The next day, Misty is the first to wake up, and the first thing she sees is Caterpie asleep, inches from her. She immediately screams in anguish, shocking Ash and Pikachu awake. Misty angrily demands Caterpie return to his Poké Ball, which upsets Caterpie so much that he crawls over and does just that. Ash demands that Misty apologize for being so mean, and tries to coax Caterpie out. Then, a wild Pidgeotto swoops down and lands in a brush, feeding on a worm. Ash puts his hat back on and scans with his Pokédex.
Wanting to catch it, Ash throws a Poké Ball, but Pidgeotto simply swats it away. Misty retorts that a Trainer needs to battle and weaken a wild Pokémon to capture it, but when she mentions that he caught Caterpie only because it was weak, the remark irritates Ash to the point where he blindly summons Caterpie to battle, without knowing that Caterpie is at a type disadvantage against Pidgeotto, though both Misty and Pikachu know. While Ash tries to figure out his mistake, Caterpie runs around, trying to avoid the Pidgeotto. Ash orders Caterpie to attack, but Pidgeotto is too strong, and sends Caterpie spiraling into a tree. It is incapacitated. Pidgeotto attempts to swoop in for another attack, but, at Misty’s suggestion, Ash recalls Caterpie to its Poké Ball, just moments before Pidgeotto can strike. The bird Pokémon instead gets its beak lodged into the tree.
Ash sends Pikachu after Pidgeotto just as it frees itself. Pikachu uses ThunderShock to hit Pidgeotto, weakening it and allowing Ash to toss a Poké Ball. The Ball takes Pidgeotto in and drops to the ground, rocking. After a few moments, the Ball ceases movement; Ash has captured the Pidgeotto. Despite the success, Misty continues to berate him for his lack of knowledge about strategy.
The Team Rocket trio intrudes on their argument, reciting their motto. They decide to target his Pikachu, mentioning its incredible power, which causes them to become distracted in a short internal argument before they decide to attack. They then send out Koffing and Ekans to battle, despite a double-team being unfair. Misty wants to jump in, but Ash doesn’t want to break the rules. Koffing’s Sludge attack blinds Pikachu, taking it out of the battle. While he hands Pikachu off to Misty, he decides to send out his newly caught Pidgeotto.
Pidgeotto dodges both Koffing and Ekans attacks before going into a Quick Attack. Ekans avoids the attack by going underground, forcing Pidgeotto to come to a sudden stop. Koffing fires a Smog attack, which Pidgeotto splits with its wings before dodging multiple Sludge attacks and Ekans’s retaliation. Despite soaring high in the sky, both Ekans and Koffing keep up with Pidgeotto. It misses a Gust attack on Koffing, which results in a harsh double Tackle attack from both opponents, taking it out. Ash recalls Pidgeotto and tries to fight Team Rocket with his fists, but James easily holds him back and swats him aside.
It looks bad for Ash, but he decides to send out Caterpie to battle. The sight of the bug simply amuses Team Rocket as they prepare to attack. Caterpie looks down, when Ash orders it to fire String Shot. The attack completely incapacitates Koffing before Caterpie muzzles Ekans. Caterpie rushes into a Tackle attack on Koffing, sending it into Ekans and thus taking them both out, shocking everyone. Meowth tries to step in, but also gets wrapped up in String Shot. Team Rocket retreats.
Ash congratulates Caterpie on coming through, and urges Misty to do the same. She agrees to pat Caterpie on the head, despite her initial discomfort, but, at that moment, Caterpie begins to sprays mist from its mouth, startling her. Ash puts Caterpie down as the mist covers Caterpie, signaling evolution. Caterpie evolves into Metapod, and Ash's Pokédex notes that it has reached this stage more quickly than any other Caterpie on record. Ash bonds with his Pokémon, which gets Misty’s approval. Despite a slight bond with Metapod, the sight of a Beedrill scares Misty as she looks forward to quickly leaving the forest. Ash is in no such hurry, however, as he seeks to capture more Pokémon.
This is the first episode in which evolution is shown.
This is so far the only episode in which a main character catches two Pokémon of different species.
According to a quote from this episode, Misty cannot stand carrots, peppers and Bug-type Pokémon.
Also, in regards to another quote from this episode, Misty mentions that she is ten years old. This was only said in the original.
This was the first time a main character catches a Pokémon that would later evolve in the same episode, the second being more than 500 episodes later in The Thief That Keeps on Thieving!.
This is the first episode where type advantages are mentioned: Flying-type moves are effective against Bug-type Pokémon.
A real animal appears in this episode, as Pidgeotto is seen eating a regular worm.
In this episode when Caterpie evolves into Metapod, it shoots a shower of white silk string from its mouth onto itself and sheds its skin in the process, similar to a real caterpillar going into pupation. Later episodes show Caterpie evolving like the rest of the Pokémon do.
Misty owns a red sleeping bag decorated with bubbles, while Ash owns a blue sleeping bag. "Satoshi" (Ash's Japanese name) appears on the name tag of his sleeping bag.
In the dub, Ash calls Misty by her name, even though she hasn't mentioned her name yet, since the scene in Pokémon Emergency! where she originally mentioned her name was in the Japanese version. Her name is mentioned in the English version, but Ash isn't anywhere near Nurse Joy when she says it.
When Caterpie is about to attack Pidgeotto, his right 'paw' is green.
When Ekans and Koffing were going in to attack Caterpie, Ekans's Japanese voice can be heard.
After Ash captures Caterpie in the beginning, his hat was backwards. When he was shown running to Caterpie's Poké Ball, it was forwards than in the next shot it was back to backwards.
In the English version, Misty reads the episode title at the start instead of Ash, while in the Japanese version, Ash reads the title.
This is justified in that, in the dub at least, Ash is busy gloating over his caught Caterpie, and thus is unable to read the episode title like he usually does.
When Caterpie is looking sad due to Misty telling it to stay in its Poké Ball, the katakana for "Ga~n" (a Japanese sound effect) moves across the screen. This was painted out for the dub.
When Misty is telling Ash that birds eat worms, there is a shot where she slaps him for putting his Pokémon in danger. This was cut from the dub.
How Misty and Ash commented on Caterpie is different between the versions (mostly due to religious censorship). In the English version, Ash was mentioning how he loves Caterpie, and Misty sarcastically responds how it doesn't take a lot to love a worm; whereas in the original version, Ash comments that he and Caterpie are the same kind of Heaven, and Misty retorts that their Heaven is her Hell.
While Ash tells Caterpie "Counter", some have taken this to mean the move, which Caterpie cannot learn. In the original, Ash told it merely to "fight back".