Ser Gregor Clegane and Mirri Maz Duur kill horses (Episode 5, "The Wolf and the Lion"/Episode 9, "Baelor")
Game of Thrones certainly has its recurring quirks: Kings rip people's tongues out like they're giving out parking tickets, and characters seem to give history lessons and/or reveal their painful backstories anytime a woman takes her top off. But what's with the hard-on for horses, you guys? Ser Gregor Clegane, the so-called "Mountain That Rides," comes down like an avalanche on the horse that fails him during King Robert's jousting tournament, decapitating it with a single blow (a feat he's said to repeat off-screen when he's killing his way across the countryside to send the Starks a message). And Mirri Maz Duur, the vengeful healer/witch who dupes Daenerys into sacrificing her unborn son to save her dying husband Drogo, slices up a sacrificial horse's jugular in spectacularly splatterific fashion. All told, there's enough equine abuse to make Luck look like My Little Pony: Friendship Is Magic.