Well Nutria, muskrat and beaver are all aquatic rodents... thats about as connected as there get. Mainly I think it's the round vs. flat tail and the presence of castor in the beaver.
Castor?
It's kinda like Cheers here on the forum. The forum is a great place to get away, we all know your name and we are glad you came.
Not everyone is glad. My troll pinched 3 points between yesterday afternoon to now. I seriously wish I knew how I pissed him off that bad.
They are fantastic pets, friendly and easily trainable. Hamsters are dicks, guinea pigs are nice enough but seem to be really bad for people with allergies. Rabbits can be hit or miss either totally mean or delightful, friendly and easily trainable. I have yet to meet a mean pet rat. (I'm sure they do exist)
I used to sing the praises of mice, but it turns out I'm only a fan of female mice. Of the 3 males I've ever owned: 1 died less than a week after purchase, 1 was a PITA and wouldn't leave my females alone or quit marking every damn thing, the last was just an asshole that wanted nothing to do with me and was a biter.
There are plenty of people with pet rats, I don't understand it, just like I don't understand why one would keep ferrets. But to each their own.
Probably because rats are social creatures. Like birds and dogs, when alone, they apply the song sage advice: "If you can't be with the one you love, love the one you're with."