Place the mouse at the opposite end of the enclosure. Just drop the mouse in, and Osiris should go for it. You can either take the hides out or leave them in. I usually take one hide out and leave one in, but sometimes I'll take everything out just in case she decides to fling rat guts everywhere. Saves me the time of cleaning everything. If it is his first time feeding for you, I would leave one of his hides in, and just let him do his thing