if you have trouble again, there's this stuff called 'make a mouse' or 'mouse maker' i can't remember, we don't have it at our store. it's liquid and you just drip some on the rat and it'll smell like a mouse.

or, if you buy live rats, get the people at the pet store to put some mouse bedding in the box, thus, the rat will smell like a mouse. but since everyone here probably feeds f/t, you're best bet is the mouse maker. or if you do pre-killed and you kill it yourself, you could do the bedding idea.