When a bubble rising in distilled water or in an aqueous pentanol-1 solution approached the air/water interface, rapid pulsations of its shape with a frequency of more than 1000 Hz were observed. In addition, the bubble bounced from the free surface, prior to its rupture or to the formation of a foam film. It is rather unexpected that the bubble's shape and consequently its surface area can vary so rapidly. It shows straightforwardly that on such a rapidly distorted interface the adsorption coverage can be very different from that at equilibrium. This fact should be taken into account more appropriately in the discussion of the mechanism of formation and stabilization of various dispersed systems (e.g., foams, emulsions).