Cows Dying Next to Fences.

I like to keep my cows in pens made out of fences so as to avoid losing track of them. Up until now, everything has been working perfectly. However, cows next to fences now die every once in a while for whatever reason.

What I expected to happen was...:
Cows next to fences would not randomly die.

What actually happened was...:
Cows next to fences randomly died.

Steps to Reproduce:
1. Put a group of two or more cows in a enclosed square-shaped area made out of twenty fences.
2. Wait.
3. Every once in a while, a cow will die. It may not happen every time this procedure is performed. Multiple attempts may be necessary.