Marvin does not speak, save for occasional crying, but he can be fully understood through thinking. He can communicate with other babies through his thoughts, but not adults or anyone capable of speaking on their own. Most of the humor comes from Marvin's very limited understanding of the world due to his early development. For example, he wonders about an approaching winter by thinking to himself "Why is now the time when people put their clothes on..." then looking out the window at a tree with shedding leaves "...And trees take theirs off".