Our cat was the same way. Mice were toys. He would catch one and play with it for days til it finally died of extreme exhaustion. My daughter locked him in the spare bathroom one time for 2 days and told him he could not come out, eat or anything til he killed it. He sometimes would bring one to me and lay it on my foot.....alive of course. He would lay down beside them with his back to them and if they moved the slightest bit he would leap in the air and slap them with his foot. He used to drive me crazy!