A rat that lives in the anus of every living being. They have extreamly large testicles which protrude from their underarms, and under developed legs, which causes them to walk on their enormous butt cheeks. A bumrat will happily eat the sharp bits in your poo and dance to dirty 70's disco music. If your bumrat dies, you die.
The french in the 100 years war fired their bumrats at the ememy, not realizing how vunerable they were when their bumrats were slain.