Worried about my pet rat

Question
I have two young rats, one of whom has become lethargic, his hair sticks up when he's at rest and his eyes are half closed. Also, he's got mucus crusted around his little nose. What could be wrong with him? What should I do? I am very worried about him.

Answer
Well - he's sick - for sure. But from what I couldn't tell you unless I could listen to him for symptoms and really take a good look at him. I recommend a vet, as soon as you can - usually by the time a rat is totally lethargic and puffy, it doesn't bode well for the future.