Following up from the Sybok rumor, on-set peeper wolf359 tells us

Several of the Enterprise command staff are allowed pets in their quarters. Lt. Uhura has a tribble, we see Chekov feeding a parrot, and we catch a glimpse in Mr. Spock’s quarters of something the set dressers called a sehl-oda — it looks like a cross between a bear trap and a litterbox, and is apparently a hygiene aid for some (unseen) childhood pet of the science officer’s…