I wouldn't lick my own keyboard, but licking my own asshole sounds interesting

You'd have to be shockingly flexible

I mean, cats are pretty smart and picky about what they do and don't do, and they do it all the time

they are also very flexible

Except in this case it's very easy to check; just drop a dosimeter in and compare it to readings from outside. And they do check, frequently, because if the water was somehow contaminated then they would have a very big problem on their hands.