Bottom Muffins

It's not often I get amused when walking around supermarkets, but this raised a smile last week - only because I had no idea what bottom muffins were.
To my mind the term "bottom muffin" can only be a some sort of euphamism Even if the muffin is treated as a noun or a verb it shouldn't be sold in supermakets in my opinion.
Obviously I had to buy them just to see what they were like. I ate two of the four, and wasn't particularly impressed. The remaining two will be becoming Swan food. I have no idea why these puerile scattological thoughts tickle me - maybe because I'm just a big kid, or maybe just because I'm a bloke. Obviously the act of going into a supermarket and having to choose what to buy is such a depressing, harrowing and traumatic experience, any light relief is welcome.