Rats

Rats are a tiny beast common in Barovia. They are also familiar to our heroes from Faerûn and the Feywild, though there is one area of the Feywild that's dedicated extensive resources to keeping a rat-free area for no apparent reason. To be fair, Feywild rats can get pretty spicy.
Much like bats, it's fucked up of Strahd to be associated with these creatures, because rats are very intelligent and adorable animals who do not deserve this abuse.