[bradleysmith]

This is also the delineator between humans and animals presented in Robert Heinlein's "Stranger in a Strange Land", and I had a knee-jerk reaction against it. It is NOT obvious to me at all.

I've seen my cats play 'jokes' on my dog. I've seen the squirrels tease her too by jumping down in the yard, then laugh-bark for minutes, taunting her from the the trees. Don't even get me started on blue jays.

I've repeatedly seen animals engage in behavior similar enough to laughter to make me doubt this claim or those making it.