u just have to know how to get the rat to like the mouse... my rat loved the mouse sooooo much, Mike would treat the mouse like a baby rat. He would clean it, pick it up & bring it to the nest & then sleep ontop of it. I was worried that the mouse would be crushed but he was ok.. he liked it... the mouse normally slept on its back while Mike lay right ontop if it.. all u could see was a pair of mouse feet & a tail... heheh