Interesting article about contagious yawning in dogs via humans, but it does not take into count that yawning is also a stress signal by dogs.
I do not doubt the validity that dogs will imitate or yawn back at humans just as they will in dogs, but I am just not convinced it is simply a contagious act and rather not a response to a stress signal that they see.
For example, Dog A is nervous and not comfortable in a given situation, so Dog B reciprocates the yawn to let Dog A know He/She understands and to relax. Either way, it is an interesting article that needs way more research to determine causality… worth a read and a little bit of a think-a-round!

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