The human eye cheats…a lot. It fills in blinds spots with estimates to keep you from confusion. If you’re looking above someone’s head, you’re using one of those blind spots.
There’s also an especially large emphasis on facial recognition hardwired into the amygdala, that we use to quickly identify potential threats.
When you put those two things together, you get some weird stuff. Try this video out. You’ll see how fast your brain will display distorted faces in favor of speed of identification over accuracy.