Reptile guy here: if you believe snakes yawn because they are tired then I've got some snake oil to sell you straight from Hiss-issippi. Snakes yawn to prepare themselves for a larger than usual meal - especially when their prey is considerably larger than their head. Unfortunately yawning can be a sign of disease. Snakes are susceptible to a ton of bacterial/fungal infections due to the type of prey they devour. I actually learned this the hard way in nineteen ninety eight when the Undertaker threw Mankind off Hell In A Cell, and plummeted 16ft through an announcer's table.