A team of surgeons at NYU’s Langone Health medical center recently managed to successfully transplant a pig kidney into a human patient without the body rejecting the organ—the first major operation of its kind, and one that apparently is raising a lot of (human) eyebrows.

Although similar tests have been conducted using non-human primates, as well as the fact that pig heart valves have been used as human transplants for some time, this is by far the most advanced procedure on record.

As reported by the BBC, said donor pig had previously been genetically modified so that its kidney would essentially fool its mammalian cousin’s body into accepting it.