Spiders and Cave Spiders glitch out when climbing walls.

If you are in a 2x2 corridor with a large room at the end with spiders/cave spiders in, and the corridor is blocked off with slabs/stairs at the end so you can hit spiders but they won't get in, just climb up the wall with the corridor, the spiders will occasionally glitch out so that they look like they're at the floor but actually stay in the ceiling of the room and you can't hit them through the slab space.