Oh they are indeed so smart, the only thing that's bad is that they only live 4 years tops being as loving as a dog, it takes a toll because you love them so much and they shine so bright and are gone so soon, but I'm grateful for the time. If ever getting them, remember, you must have at least two (three is better) as they're social and they do need companionship, if not they don't develop their character as it should be and are just sad and depressed. It's natural to be freaked by any wild animal, if a person comes dirty out of the sewers and feels menace I wouldn't go and touch it, we must remember though that dirt down there is ours :( they just fend as they can. Rats are often blamed for the plague but truth is that they were not the carriers but the flees that were in ALL hot blooded beings back then including people. As a curiosity Rattus Norvegicus (common rat) was resistant and helped to displace other rodent species, helping (oh the contradictions) to erradicate it XD by displacing other animals more susceptible to have flees. Really they are amazing, with a little patience you can potty train them, teach them to fetch a ball, come by their name. I had a hamster, she was so beautiful and special but she chewed "everything" ratties can be taught not to, hahah they will gnaw things sure, but they can be trained to be on open cage under vigilance. hahah I sound like a Crazy Rat Lady hahah :) well hahah I try my best to spread some information about it.
Pd. I studied Molecular Biology but I could never hurt one... now I'm a pro-them and try to make people aware of how many lives they have saved as involuntary research subjects. We should be grateful.