Laughter occurs when something unexpected disrupts our assumptions. A good joke catches us off guard, forcing us to momentarily step outside our usual thought patterns. This expansion of perspective is why humor is a powerful tool for learning. When a person laughs, he becomes more open, more flexible in thought, and more willing to see things in a new way. This explains why Rabba began his shiur with milsa d’bidichusa, humor, making his students laugh—because an expanded mind is better prepared to absorb wisdom.
The gemara, when discussing the minimum size of a Sukkah wall, refers to an expanded tefach as a טפח שוחק, a “laughing tefach.” Rashi explains that a standard tefach is measured with four fingers pressed tightly together, while an expanded tefach is measured with the four fingers slightly relaxed and therefore somewhat separated, making this tefach slightly larger. The expanded tefach is called טפח שוחק, which signifies expansion. In the same way, when we make others smile and laugh, we help them open up and expand.
