I don't see how it could be fake. I assume it was an accident, but why would they continue like nothing happened? And why would they put it in the movie? And why haven't I seen anyone mention it?
There are still some older movies out there that show animals being killed for real.
The most obvious one is the ox being killed at the end of Apocalypse Now, but it was a real tribal ritual that was taking place and Coppola just filmed it and put it into the movie.
And though I can't name one just now, I have seen a few movies that show chickens having their heads cut off.
"Food of the Gods" (1973) has giant rats that are obviously normal sized rats in miniature sets.
Also obvious: they were being killed probably with BB guns when the characters shot them. You could see holes opening up in their bodies and pieces of their heads getting blown away.
A FEW YEARS AGO I ADOPTED SOME HENS...I NO LONGER EAT CHICKEN OF ANY SORT...ONLY MEAT I DO EAT IS THE OCCASIONAL BEEF...THAT WILL BE GONE SOON TOO I IMAGINE...I USED TO LOVE MEAT...ANIMALS MAKE IT WEIRD.