A behaviorist will respond that there is a behavior: saying they are in pain!
Putnam then came up with super-super Spartans, who suppress all outward behaviors of pain, including talking about pain. In this case, there is absolutely no behavioral differences between someone in awful pain and someone in no pain at all. A behaviorist would then say that there is just no pain in the person who is thinking about the awful pain but not showing any overt behaviors. Putnam thinks this is ridiculous. Someone can have a mental state like pain without showing pain-associated behaviors. On the flip side, someone can fake pain behaviors when there really is no experience of pain!.
Another argument against behaviorism is that if mental states are just behavaiors, then someone else other than myself can be in a better position to know what my mental states are than I am. Indeed, logical behaviorism entails the fact that outside observers are able to tell what your mental states and experiences are. Logical behaviorism entails that an individual does not have special access to knowledge about his or her mental states. If you are a logical behaviorist, you have to accept these consequences. If you think these consequences are ridiculous, then you cannot be a logical behaviorist.
Putnam objects to logical behaviorism on other grounds, as well. He says that behaviorists make a confusion similar to confusing symptoms for a disease. A disease causes symptoms but the disease itself is something more than just a group of symptoms. Similarly, a mental state such as feeling the emotion of love or having a desire to punch your little brother may cause certain behaviors. Just because we know what the effects or consequences of certain mental states are does not mean that we know what the actual mental states are!