 They know that your eyes are forward facing. The mask makes your eyes look even bigger than they really are. They're seeing you as a bigger predator than you are, especially if you're kind of going more vertical in the water column. So if you can make eye contact with them, they know that you're a little scary. They can tell you're not moving like a seal. They're like, what the heck is this thing? This is clearly large. It's not prey. I'm not going to eat it. I think I'll pass on that. I'll get out of the water when I see a shark.