It's a surprise tool (Patreon)

Tavik getting the shivers and puffing up his fur when surprised is not a particularly common trait for a venlil, who'd rather make themselves smaller when under stress, but it certainly makes him more expressive in human eyes

Speaking of which, the horizontal/rectangular pupils make for very striking expressions when shrunk, while not even being clearly square when dilated and relaxed

https://www.reddit.com/r/HFY/comments/u19xpa/the_nature_of_predators/