I've had many pet rats...show rats, pets, even feeders I kept for pets and they were almost always excellent pets. I had one bad experience with a large, old, feeder male that I believe went blind and bit everything that went into his cage (like my children's fingers), but on the whole, they are clean, friendly, and intelligent.
Most would come when called by name, play, do tricks, and were generally healthy. No vaccinations were required.
The only thing they ever had a problem with was mites, one time. Then I bought a 'bird mite' tin and hung it in the cage which rid them of the mites right away.
As far as litter training...my rats always wanted to use thier cage. I used cedar shavings as they smell good. I showed my rats at some professional rat breeders shows in California as I had Siamese rats but others were more into than I so we never got any ribbons.
Otherwise, they do make very nice & quiet pets.
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