Donatello and April make a bizarre discovery while investigating a scientist's disappearance.
This episode provides examples of:
- Bitch in Sheep's Clothing: Dr. Falco
- Centipede's Dilemma: Mikey has this problem when he starts thinking about how to fight without thinking.
- Chained by Fashion: The mutant monkey has shackles on his arms, legs and neck.
- Combat Clairvoyance: The mutant monkey is psychic and later Dr. Falco.
- Comically Missing the Point: April in her conversation with Splinter, with a side of Innocently Insensitive.
- Crazy-Prepared: Donnie's chart about how to hang with April.
- Don't Think. Feel: The Aesop of the episode boils down to this. Splinter tells Donnie that he needs to learn how to "fight without thinking".
- The Empath: The mutant monkey. Also, April and Splinter.
- Empathic Environment: A rainy thunderstorm breaks out when Falco is revealed to be evil. As soon as the Turtles defeat him, all signs of a storm are gone.
- Extraordinarily Empowered Girl: April turns out to be this.
- Expy: Dr. Falco is one of Herbert West from the Re-Animator films, right down to having the same actor.
- Implausible Boarding Skills: Mikey combines this with Roof Hopping.
- Kick the Dog: After gaining psychic powers and defeating all four of the turtles with little effort, Dr. Falco rubs salt in Donnie's wound with this comment:
Dr. Falco: By the way, do you really think you have a chance with April?
- Lap Pillow: April lets Donnie rest his head on her lap after he gets beaten up.
- Mad Scientist: Falco
- Maniac Monkeys: Even after the Turtles learn he's not just a mindless monster, he's still quite dangerous when angered.
- Metamorphosis: Dr. Rockwell, from human to mutant monkey.
- Mid-Season Twist: April begins her training with Splinter and the Turtles acquire and actually manage to keep a live canister of Ooze.
- Red Eyes, Take Warning: Falco's eyes become bloodshot after he injects himself with the psychic neuro-chemical.
- Replacement Goldfish: Played pretty straight when Splinter asks April to train as a ninja because of her gift of empathy. Especially notable because afterwards it's obvious he's thinking of his lost daughter, Miwa.
- The Reveal: See Wham Line.
- She's Not My Girlfriend: Donnie says this again, only this time it was Raph who did the teasing.
- Sinister Silhouettes: The scene where Falco extracts the psychic neuro-chemical from Monkey Rockwell's brain.
- The Speechless: The monkey is the only mutant in the show so far who can't talk.
- Stalker with a Crush: Donnie makes a flow chart with every conceivable excuse or reason to hang out with April for any possibility. Every possibility.
- Stealth Insult: When Splinter explains how to fight without thinking to Donnie, he uses Mikey as his example.
Splinter: You see? Mikey does not think.
Mikey: Thank you.
- Tail Slap: After Splinter demonstrates Mikey's ability to dodge his attacks without thinking, he compliments him. Then he gets Mikey at the last second by tripping him with his tail.
- Theme Tune Cameo: When Donnie unveils the T-Phone, it's accompanied by the theme tune performed in the form of a ringtone.
- Was Once a Man: Dr. Rockwell
- Wham Line: "I think this IS Dr. Rockwell."
- Later, "...then what broke out of the cage?"
- Would Not Hit a Girl: Played with. The monkey beats the tar out of Donnie and starts to go after April. He gets as far as grabbing her and roaring in her face, but backs off after she talks to him. It's later revealed that the monkey was reading their emotions, so he was hostile when Donnie was hostile and calm when April was calm. Her gender had nothing to do with it.