Trying to get a cat to kill the mice can be hit or miss because it all depends on the personality of the cat and what environment the cat grew up in.
If you have a cat that has always lived indoors and never seen a mouse before, chances are they'll be too stupid to know what to do with the mouse during their first encounters with one. They would either just stare at the mouse and think "Ooo, what's that?" or they'll think "Oooo, it moves! It must be a toy!" and would chase it around but not kill it. Sometimes they'll kill it and then go "Bummer, it don't move no more!" and leave it there.
Yes, cats can be dumb like that. Thankfully I have a cat that has spend most of her days outside so she knows what to do with mice. Unfortunately she likes to torture them for a good 15 minutes before killing it and she sometimes just leaves it dead instead of eating it.
The cake is a lie... THE CAKE IS A LIE!!!!!