Rats have boobies too!
They have LOTS of boobies, so a rat bra is a far more complicated construction than, say, human bras, or monkey bras.
Marsupial bras don’t even have to exist, as marsupials keep their boobies in their pouch.
The pouch is nature’s bra.
(NB. Rats do actually have 8 nipples. This rat has the full amount, but only six of her boobs are in the picture)