Right, here goes:
Once upon a time all the dogs went to a big, grand, posh ball. On entering the room they had to hang up their bottoms because it was so posh. Hooks were provided by the door for the bottoms. The ball was in full swing when a fire broke out. All the dogs rushed to the door and just grabbed the first bottom they could find. Luckily they all escaped unhurt, but needless to say, most got the wrong bottom, which is why to this day they sniff each other’s bottoms, trying to find theirs.
There’s a children’s book with the story: The Great Dog Bottom Swap by Peter Bently.
So this is the explanation dragonfly!