FIG. 1.

Illustration of instantaneous images of the expelled respiratory liquid and its breakup morphology. (a) When a sheet of sputum is expelled from a human, a liquid sheet gets destabilized to (b) form a drop (effect of the K–H instability). (c) The respiratory drop further gets “film ruptured” into ligaments (effect of the R–T instability). (d) The ligaments due to the effect of surface tension break up into (e) smaller drops (effect of the P–R instability). Note that these images (a)–(e) are obtained from a blown soap bubble with gravity pointing to the left and a mere representation of the intermediate events that occur while expelling the respiratory liquid. Likewise, the depicted images are highly exaggerated and not to the scale of a human mouth. The time interval between the two images is not equal.