“The Hunting” by Doris Beetem.
Finished “The Hunting” by Doris Beetem. Part of the Star Trek: The New Voyages short story collection.
It was short. Even for a short story.
Spock goes on a ritual hunt called the Mok farr, where a Vulcan must pursue a dangerous animal for the purpose of subduing and mind melding with it to get an understanding of its bestial nature. To understand the animals base emotions reminiscent of a Vulcan's own violent emotions. And yes, I'm cribbing a little bit from Memory Beta, because it's really that brief.
Anyway, McCoy finds out about this, and decides to go with him, because he thinks Spock might need help.
Spock finds and melds with a predator called an owltiger. Apparently it got the name because it's a tiger, but its ears are reminiscent of an owl. Something goes wrong. The owltiger takes off, and so does Spock. Apparently the mind meld didn't completely finish, and now Spock thinks he's a tiger. A tiger that's wildly confused that its paws are now hands.
McCoy needs to track him down, and entice him to return to camp until the affect can wear off. It's not really hijinks. It's a fairly interesting exploration of the Vulcan psyche, and an exploration of the relationship between the two.