There are both primary reinforcers and secondary reinforcers that we speak about in dog training. A primary reinforce is something related to the senses or to the biology of the dog. Treats are a good example of primary reinforcers, but keep in mind that visual stimuli is also a primary reinforce. Some breeds, for example, the sporting breeds have a strong visual sense and a strong prey drive. That drive can be so strong, it overrides a favorite treat. This might be a good thing, depending on how you look at it. Just be aware of it and don’t write the dog off as “stupid” just because you don’t understand the dogs drives.