Two gorillas were witnessed doing the deed at a zoo in the Netherlands. Visitors spotted the frisky pair, identified by officials at Rotterdam Zoo as Aybo and Thabo, engaged in various positions.

Witness Shirley Kroose told Metro the two apes didn't seem to mind the audience—and she wasn't put out, either. "They were doing some adult things with each other playfully," Kroose said. "Before and after they were running around with some toys they were given by the zookeepers. It was great watching these two boys having fun together. It was very unique capturing them on camera."

Homosexual behavior is not uncommon in the animal world, where sexual contact can help cement relationships and relieve sexual frustration. There have also been numerous cases of animals choosing to bond with members of the same sex despite the presence of suitable partners of the opposite sex.

In 2016, researchers at the University of Western Australia documented homosexual behavior in female gorillas for the first time: Looking at a group of 22 females in the wild in Rwanda, they found 18 engaged in frottage and other same-sex activity. "Given that these observations come from wild groups, not gorillas held in captivity, it is obvious that homosexual activity is part of the gorillas' natural behavioral," said Professor Cyril Grueter.