For some exercises, we will show the dog how to do the behavior (ie "Sit") by having them follow a food lure (pea-sized treat). Many dogs will do this readily, but some think it might be a trick! With practice, they will see that there is no catch.
Imagine the treat is a magnet and your dog's lips a refrigerator. The treat should touch their lips like sticking a magnet onto a refrigerator!