The bug
If a strider is facing down, their "heads" would go through their legs. This can occur naturally when a baby/adult strider looks down while riding another strider.
MC-198165
Striders "heads" would go through their legs if looking down or up
Open
6
(Unassigned)
Community Consensus
Gameplay
Low
Textures and models
1.16.2, 1.16.3 Release Candidate 1, 1.16.3, 1.16.4 Pre-release 1, 1.16.4 Pre-release 2, ..., 21w07a, 21w11a, 21w15a, 21w17a, 1.21
Retrieved
Can confirm, also happens when they look up.