this requires a bit of a set up to do, since it's more of a situational bug.

first, find/make a village with a naturally spawned iron golem. get his health down so he can die in 1 hit.
second, tame a wolf.
third, punch a villager.

the wolf will then kill the villager, and after that the golem will rush after the wolf and attack it.

if the wolf manages to get a hit in and kills the golem (happens from time to time), it'll walk up to the golem last position, start looking up and freeze as long as it's standing. making it sit will temporarily cancel the freeze so it'll look at you and passing mobs, but once you make it get up it'll resume the stare at golem's death position.

it won't follow you, it won't look at anything, it won't wander around. it'll just keep on staring at the golem's death position infinitely. if you push it away, it'll run back to the golem's space and then keep looking up. sometimes its head might start spazzing out, as if it had a seizure.

basically, whenever a tamed wolf kills an iron golem who defends the village from it, its ai will get stuck in some sort of infinite loop.