The bug
When you push against the llama's head while it is mad at you, the spit just goes through you. I have tested in different gamemodes (easy, normal, hard). Also, it does not matter whether the player is facing towards, away, or sideways. Just the distance between the player and the llama head matters.
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Can confirm on latest pre-release
Can confirm for 20w46a.
Can confirm in 20w51a.
Can confirm in 21w03a.
Can confirm in 21w05b.
Can confirm in 1.16.5 and 21w08b.
Isn't this same with MC-125936?