When is yawning contagious?

When is yawning contagious? – Apparently, yawns are most contagious at 7:30 pm. But, why? No one knows for sure even why we yawn, let alone why we yawn after seeing someone else yawn or even simply after seeing someone pretend to yawn. (If it were a change in air pressure or CO2 levels in the room, you wouldn’t expect that to happen). More to the point lots of animals yawn, babies yawn, we do yawn when we’re tired, but we also yawn after a good night’s sleep. It’s a puzzle, a mystery, a paradox, and a conundrum. Now, think about your mouth opening, your arms stretching above your head, your head thrown back…did you yawn?