Dogs die in walls

I have alot of dogs and noticed they took damage and wondered how this happend.
What i did was i came back and forth and checked and walked into one of the dogs that looked odd. The dog went into the wall and took lots of damage.
I Broke the Blocks and saved him.
the Room in about 5 Blocks width by about 20 Long and had about 20 or more dogs in it. I didnt take snap shots sadly.