Here's my contribution to this thread.
Was at the San Diego Zoo (a breeding zoo, as they kept telling us!) last month. It was on a Monday, which is kiddie's day, and there were lots of children and parent/teachers standing about, watching the monkey cage. Much was being said about this "baby"monkey, who was aggravating the heck out of what was assumed to be the "mommy" monkey. Baby was pulling on mom's tail, etc, etc. Finally "mommy" got mad and started fussing back.
Parents etc. were making comments about how the mommy monkey was going to scold the baby monkey, etc. Baby monkey then actually crawled all the way up mommy monkey's tail, whereup "mommy" sat "baby" on his/her lap, and proceeded as shown below.
There was dead silence from the human audience. Particularly the parental units. 
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