That horrifying shriek of pain Splinter lets out when Shredder uppercuts him at one point, all while the turtles and April watch but are unable to help, due to Splinter closing them off so they could escape.
Eric Sacks gleefully admiring the three turtles he had kidnapped and rigged to a machine to drain all their blood.
Karai demonstrating the effects of Sacks's toxin on a poor bastard Foot Soldier in front of the captive Turtles, resulting in his skin melting off as he convulses on the floor.
The cracking noise Raph's shell makes when Shredder is stepping on it. A little more pressure and he might have split wide open. His response after surviving the ordeal?
April's first meeting with the turtles is this from her perspective. She's clearly terrified, and you realise that if they wanted to kill her, they could have.
Leo tells April that if she tells anyone about them, they'll find her. After that, Raph takes out his sais and twirls them. Yeah, they just gave her an Implied Death Threat.
