So I frequent the local family owned pet store where I got my rats to look at all the cuties they've got jumping around in there, and I noticed some of them look like they have serious ear mites. They have lumpy spikey looking ears. But some rats in the same cages look totally fine, and my girls have been pronounced healthy and mite/parasite free by our vet. Do mites not infect every rat they can? I would've thought the entire population would have mites if one did, but some of them seem to be fine and others look awful. Just curious if anyone knows why...