Floating Cow Heads

I was out exploring, just hiking in a random direction in hope of finding something interesting. At one point I happened across groups of what appeared to be the heads of cows floating just above the ground. They mooed, walked around and behaved like normal cows, save for lacking anything other than their heads. As far as I could tell, their bodies simply appeared invisible. I had encountered cows before in this particular world, but they didn't have this issue. Might this have something to do with my texture pack? Or is it inherent to the base game?