3 of mine hump. Diesel, Lilly, and Lola. The girls seem to do it to mimic Diesel, because they only do it after watching him bug everyone and everything with it. If I see them doing it, they get scolded and must stop. Sorta like a toddler. When my boys were little, if they were playing with their "toy", I told them no-no and they had to stop. My grandma has a stuffed dog for her Murphey (Joe's brother). He is fixed and humps the daylights out of that thing. She lets him drag it out in the middle of the livingroom right in front of company
She gets upset if anyone scolds him because its "natural". My mom puts it up when she goes to visit
It makes everyone very umcomfortable to have a conversation with a dog "making love" as my grandma calls it, to a stuffed animal right next to them.