Interesting test. I thought of a "red hammer" so I looked it up on the internet and found this explaination:
A prototype is the best example of a natural concept. (see Concepts)
Example: Try this trick on your friends. Have them sit down with a pencil and paper. Tell them to write down all the numbers that you will say and the answers to three questions that you will ask. Recite about fifteen numbers of at least three digits each, and then ask your friends to write down the name of a tool, a color, and a flower. About 60 to 80 percent of them will write down "hammer," "red," and "rose" because these are common prototypes of the concepts tool, color, and flower. Prototypes come to mind most easily when people try to think of a concept.
Source: http://college.hmco.com/psychology/bern ... /ch08.html