Poor Pavel Chekov. He finally gets out of the navigator's chair he was stuck in for two seasons on the show—but as soon as he lands a new gig, he gets a super-creepy space eel stuck in his ear.
It's a raw deal, especially for a guy who's so gregarious and friendly. That friendliness helps us understand just how horrible Khan is when he sticks that eel in his ear—it makes Khan look like the kind of monster that would torture puppies.
And it also lets at least one of the supporting members of the crew get in on the action. We love Sulu and Uhura and Scotty, but frankly, they're just moving scenery in this movie (which is why they don't get entries here: forgive us, Trek faithful). Chekov gets some skin in the game: he's transformed into Khan's hapless zombot and forced to lie to Dr. Marcus in an effort to secure Genesis for his master.
It's a tough road, but luckily for him, Kirk totally gets it. When some madman sticks a mind-control worm in your head, you can't be held accountable. That's why he not only forgives Chekov for pulling a phaser on him, but he doesn't hesitate when Chekov comes back looking to help out in the battle against Khan.
CHEKOV: Could you use another hand, Admiral?
KIRK: Man the weapons console, Mister Chekov.
Nothing more needs to be said, and all is forgiven: another one of those signs that Star Trek II understands how much the friendship of these characters matters to the fans. That's worth the odd space eel or two, and we thank Mr. Chekov for taking one for the team.