I actually would have thrown that rat out. Meat's okay after 3 days in the fridge, but that's CLEANED meat. You know how big game hunters clean their animals and throw out the intestines as quickly as possible after they shoot it? Because the acid in the guts will rot the meat much faster than it would otherwise? A rat is whole, guts and all, so it'll spoil faster than a chicken breast or a steak in the fridge.

And I bet that's why it exploded in the hot water bath, too.

(But I've fed my guys exploded mice that I've forgotten about for a few hours, or left under the heat lamp for a bit too long. And they've been perfectly fine. Generally, if it's questionable but not obviously bad, I let them be the judge. If they take it, great! If they give it the evil eye and duck their heads, then I pitch it.)