Laughter

Only humans laugh, animals do not. This is because animals are from the physical, temporary aspect of creation. Laughter is not found in temporal things. Man can laugh as well as cry. Laughter comes form his spiritual/eternal side, crying from his physical/temporal side. With the destruction of the Temple, our sages taught us that one should not overly engage in laughter. As the physical aspects of the world are now in ascendancy, laughter cannot be the primary emotion. Only אז ימלא שחוק פינו, then, at the coming of Moshiach, can our mouths be full of laughter. This is also the reason why a baby cries as it is born. The soul has until now been in a totally spiritual place. Its introduction to the world of the physical, and a minimizing of the soul's connection to the spiritual, brings about crying.