Don't feel sad for this horse that's being shot by a machine gun. He'll get right back up.

“Assassin’s Creed Brotherhood” is an immensely satisfying, well-designed open-world game with a puzzling design feature: Its horses can’t die.

Unless you go out of your way to try to kill the horses of Renaissance-era Rome, their immortality isn’t that noticeable. The design quirk really doesn’t jump out until you start playing the “Leondardo’s War Machines” side quests, one of which requires players to destroy two prototype machine guns.

I’ve posted a video of the mission below. The horsepocalypse begins around the 5:10 mark. Note the ridiculous way in which the ragdoll physics sends the horses cartwheeling into a heap, only to get right back up and gallop away.

The horses of “Assassin’s Creed Brotherhood” are not the majestic yet fragile beasts of Churchill Downs or Golden Gate Fields, who have to be euthanized if a fracture forms on their leg. These are indestructible mounts worthy of the Terminator or Monty Python’s Black Knight.

The machine gun sequence circles a pimple. It takes a minor flaw that only a handful of players might notice, and draws a big red circle around it. The army of everlasting equines produces bigger laughs than most games that go out of their way to try to be funny.

It’s hard to imagine why “Brotherhood’s” horses are unkillable. Was Ubisoft Montreal worried about offending PETA or another animal rights group? “Red Dead Redemption,” released six months before “Brotherhood,” killed off horses by the bargeful, and even featured undead ungulates in its downloadable content. The world kept turning on its axis, and Rockstar Games made a ton of money with little to no outcry over the massacre of virtual steeds.

If anything, Ubisoft’s hooved marvels actually promote cruelty to animals. After the machine gun sequence, which I tackled very early in the game, I became obsessed with trying to kill horses. After some trial and many errors, I concluded “ACB” won’t let players ride or push their horses off of cliffs.

Stumped, I rode my mount to a dead-end alley, cornered him, and did my best Jack the Ripper impression with my heaviest sword. Though my horse whinnied and neighed, kicked, bucked and fell down on the street, he always got back up, ready for more. So I hit him again, and again. Eventually, long after I concluded the horse I rechristened Chumbawamba was, in fact, invincible, the little weasel got around me and started to flee.

No matter. I simply whistled for him. He came galloping over, and I hopped on and rode off into the countryside as if nothing had ever happened.