Food frozen inside ice cubes can provide great stimulation for your pet. Freeze a small piece of cheese or meat inside an ice cube and leave it in your pet's dish. He will lick away until getting to the prize inside, especially if you dissolve a bouillon cube in the water before freezing. A raw egg still in the shell can be very stimulating. Left in a pet's dish, many do not at first know what to do, but soon figure it out.
Mirrors can be great fun for pets, who often think their reflections are other animals.
Changing the time of feeding or the location of your pet's food dish will stimulate his senses and get his mind working. Every so often, move the dish to a different location, and watch what happens at feeding time. Also, feed an hour later or earlier on a random basis. Dog crates and kitty condos are great additions you can make to your home. The crate, in addition to helping with housetraining, can provide him with his own place to rest.