The horror-film wheels of Jordan Peele’s “Get Out” really get greased in the film’s pivotal home brain-transplant scene, in which Dean Armitage (Bradley Whitford) deftly scalps the head of a blind art dealer in preparation to swap his brain with that of captive Chris Washington (lead actor nom Daniel Kaluuya).

The real horror, however, might be that brain transplants are actually possible in the real world.

Jordan Peele fell down an internet-research rabbit hole in 2016 after news broke that Italian surgeons had successfully grafted the head of one chimpanzee onto another’s body. He started researching the concept, and found a New York Times article from way back in 1982 when a scientist at New York’s Mount Sinai hospital grafted one piece of a mouse’s brain successfully into the head of another’s. That experiment is eerily similar to Whitford’s own home skull switcheroo.

“It all just kind of scared me,” he says, adding...