i was herding chickens near my base which is surrounded in cobblestone walls.

when the chicken had to navigate its way around the wall, its head would appear through the other side.

once this happened, the chicken was unable to move away from the wall.

it could walk along the wall while it's head was stuck in it.

the player has to manually remove the chicken from the wall, and subsequently learn to avoid having the chicken clip through it.

steps to reproduce:

build a cobblestone wall

spawn a chicken

herd the chicken with seeds

position the player so that the wall is in between Steve and the chicken

allow the chicken to run into the wall in it's pursuit of the player

move the player away from the wall and attempt to get the chicken to follow in another direction

observe that the chicken will not move away from the wall

not sure if other mobs are affected by this.