Pink. Sock.
Long story short (and WILL NOT be adding pictures), anal fisting is taking your butthole places it wasn't meant to go. Vaginal fisting on the other hand is a little less dangerous because twats were meant to stretch. It's their main purpose for most people.
Now, what happens when you stretch something out that wasn't meant to be stretched to such limits? If it's your anus, it falls out. And looks like an angry, fleshy rose. Something out of Dante's Inferno. It's ew.
/thread