The bug
Mobs in boats move / shake their head when attacked.
Note: The mobs sometimes rotate their heads to the very left or right as well without rotating the boat before, see MC-90148.
How to reproduce
Put for example a sheep in a boat
/summon boat ~ ~ ~ {Passengers:[{id:sheep}]}
Hit it without killing it
Related issues
Attachments
Comments


This will work for any mob in a boat that will "panic" when hurt. It is confirmed for 1.9.3 Pre 2
Can confirm for MC 1.12.1.

affects 20w18a
Can confirm in 20w48a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Video attached.
Can confirm in 21w07a.
Can confirm in 21w11a.
Affects 1.20.4. Requesting ownership of this issue due to lack of updating the issue with affected versions.