A recent BBC science article stated the following about contagious yawning:
A susceptibility to contagious yawning may actually be a sign of a high-level of social empathy.
Although many species yawn, only some humans and possibly their close animal relatives find yawning infectious, suggesting the reason is psychological.
I beg to differ. I have seen contagious yawning in horses on several occasions, and they are not closely related to humans. Just two days ago, my horse yawned two big yawns while standing in the aisle of the barn. I had to chuckle as I immediately felt the urge to yawn, and did so. Then the horse in the stall to my left yawned. Then the horse across the aisle yawned. I do not see horses yawn often, and to have three yawning all at once was unusual.
On another occasion I "made" a pony yawn, as a bit of an experiment. He was in his stable, and I stood in the aisle across from him and pretended to yawn several times (by the third time, it was a real yawn - if you think about yawning long enough, you start to feel the urge). A moment later he joined in, yawning several times.
I think we tried this experiment on our cats a few times, but with less evident results. I bet it works on dogs, which tend to pay a lot of attention to what humans are doing. Try it on your pets and let me know what happens.