I found a bug when you attach a lead to a horse and fly above it, forcing its head onto a solid block.
What I expected to happen was...:
Him to not take damage.
What actually happened was...:
He began to suffocate in the roof.
Steps to Reproduce:
1. Spawn a horse and build a roof.
2. Leash the horse and force its head into the roof.
3. You should hear the horse taking damage.