You have most likely come across a small surprise when putting on your slippers or your sneakers—whether it’s your cat’s favorite jingle ball, or a less-than-pleasant dead rodent. This can be more than a little puzzling at first because you wonder how on earth it got there, and then, once you’ve determined that this is your cat’s doing, you begin to wonder again what exactly your pet’s intentions are behind hiding their ‘treasures’ in your shoes.
Source: Why Does My Cat Put Stuff in My Shoes? – Bela Pets