When I was growing up, and my dad and uncles were into car repair, front-wheel-drive was relatively rare, and most American cars had front engine and rear drive wheels. There was a very important part called the “differential” which sat at the rear end of the drive shaft and connected also to both sides of a rear axle and the drive wheels. The informal term used for the differential was “rear end”.
Since “rear end” was also an informal substitute for “butt”, there was occasion for many a scene just like the one in this cartoon.
This is inflation on count-to-ten.
Jane: I once went on holiday and pretended to be twins. It was amazing fun. I invented this mad, glamorous sister and went around really annoying everybody. And d’you know, I could get away with anything when I was my crazy twin Jane.
Sally: But you’re Jane.
Jane: Kinda stuck. It’s a long story.
And there was a sequel:
, or use the 
