(Probably related to or dupe of MC-7464; I created this as a seperate issue due to how mobs != TNT)
I had finished making an underwater tunnel to connect a couple of islands, and wanted to bring a couple cows home from the other island. So I forged myself a couple extra minecarts, hearded a pair of cows in, and ran them to my base minecart station.
I had a spare room already dug out, and decided to store the cows there. I figured the easiest (and safest) way to transport the cows there would be the minecarts they already were in. So I dug up a spiral around my central column (measuring 3x3 spaces; the center space is ladder, the other 8 are dirt, but I digress), hugging the corners to save space and track. I then start pushing one of the cows up.
flashes red "Mooo!" flashes red "Mooo!" drops meat
It didn't happen that quickly, however. I had ended up determining what exactly was hurting the cow, it was the turn it had to go through. Specifically, a turn where there are nontransparent blocks on the inside of the turn. The other cow (and a third one I later got) safely made it up the slopes when I revised the path to avoid the hugged turn.