spock goes into a volcano because he saw a cool spider. however, spock gets stuck. kirk goes in the volcano to save spock. at this time, kirk was too busy getting gay backrubs from spock to notice that a spider was biting him. they safely leave.
the rest is irrelevant to the clue
later that day, the gravity aboard the enterprise malfunctions. most members of the crew start to float around, but kirk does not. he is concerned, but a graviton scan does not find anomalies. the gravity is fixed.
that night, spock notices a bite on kirk, and advises kirk to go to doctor mccoy.
(i think i will continue this)