Dave here. Just lucky for you that we're on the case looking for answers. Turns out science knows why. Researchers say that your core brain temperature rises when you're tired, when you're bored or when you have an infection. Yawning has a cooling effect on your brain, preventing it from getting overheated, which can diminish alertness.
What happens when you yawn is that your mouth gapes open and you inhale deeply, then briefly exhale. During this time, the muscles around your skull contract and stretch and you take in that ambient air. That's when new cooler blood is pushed toward your skull as warmer blood is pushed out. (And I thought WE JUST YAWNED!)
Question? Can you catch a yawn? Yup! And there's research to back that up, too. The experts say it's all about empathy. Say they, "If one member of the group yawns, it's indicative of something that YOU should be doing."
Can you catch a yawn from your pet? Visa versa? And do yawns stop at dogs and cats? I think our guinea pig can yawn...or is he just bored?
And one final thought...I yawned while I was preparing this blog several times when I read the word "yawn." Did YOU when you read this? What's up with that? DaveT