What are they doing?

A woman and her little boy were walking through a park in New York and they pass two squirrels having sex.

The little boy asks his mom, "Mommy, mommy, what are they doing?"

The lady responded, "They're making a sandwich."

Then they pass two dogs having sex and the little boy again asks what they were doing.

His mother again replied they were making a sandwich.

A couple of days later the little boy walks in on his mother and father and said "Mommy, Daddy, you must be making a sandwich because, Mommy has mayonnaise all over her mouth!!!"