In Passions of the soul (French: Les passions de l'âme), the last of Descartes' published work, completed in 1649 and dedicated to Princess Elizabeth of Bohemia, he writes:
"Now although Laughter might seem to one of the principal signs of Joy... we find by experience that when we are now extraordinarily Joyful the subject of that Joy never makes us break into Laughter, and we cannot even be inclined to it by some other cause so easily as when we are sad."
The reason for this might not have anything to do with our lungs being so swollen they cannot be swollen by renewed surges of sentiment ~ not that this isn't the physical sensation that accompanies this state ~ but rather because in this state all the particles are co-participating in an elated state of jubilation that needs no accompaniment ~ no further embellishments.
Perhaps there are those moments when we are so utterly enveloped in sensations such as those that arouse the entire entity toward a rapturous state from which Joy is felt in every particle of our existence, there is no room for laughter... as all the molecules or particles are co-participating in an all encompassing and all-consuming energetic experience.
Whereas when one is sad or otherwise fragmented within oneself ~ anomalies, inconsistencies, exaggerations, lesser -vs- greater expectations, and so on... all contribute to a state of mind that mistakes nervousness for excitation, drama for intensity, and forgiveness for acceptance.
Rather than flippant or frivolous behavior, when the true passions of the soul are ignited, the abundant intensity easily lures the body into a vivacious state high-spirited exuberance.
Here, anything that is a passion with regard to one subject is an action with regard to something else ...
As with the second scenario, the sprite and delicate, airily and breezy footsteps pirouette themselves around muddied bootprints, dancing on solitary fibers that ebb and flow in a way that no other dance form can emulate.
So skimpy are the other threads that they might be mistook for threads of reason.
The combination of which can harmonize the body and soul in a way that duality dissipates into complete and utter unity. Perhaps this duality of existence was mistook, perhaps it is an entirely different state accessed by the most sensitive and subtlest, profoundly feeling thinkers... such as were Descartes and Princess Elisabeth of Bohemia. No wonder they corresponded from the day they encountered one another until the day he departed.