That was a joke. Let me tell you the reason why it is funny...
What gets wetter the more it dries?
Q: What gets wetter the more it dries? A: A towel.
In my opinion this is not actually a joke, but a riddle. I found it on a website on the internet labeled as a joke. The "joke" centers around the fact that the reader is supposed to assume that "dries" in this sentence is a reflexive verb. The way that it is supposed to be understood at first glance is "What gets wetter the more that it becomes drier." instead of "What gets wetter the more things that it dries". The moment that the riddle is answered the listener has to reevaluate their understanding of the verb dries.