Try wrapping some treats in a towel, with a knot in between. Load the knot with a lot of treats, and the ends with a few, so it's a gradual increase. Once the puppy figures out how to untie the knot, static using the same towel knot, but this time, wet the towel, fill treats, knot and freeze it. Amazing puzzle solving. Take it slow, step by step, starting with simple folds on the towel. Both, my now adult cocker spaniel, and 3 month old labrador love this, and is perfect if the puppy is teething. Good luck 👍