The hot chocolate effect, is a phenomenon that is reproduced by stirring a hot liquid and adding soluble powder. Tap the edge of the cup repeatedly one by one the spoon, we notice that the sound produced has an increasingly louder tone. This effect is explained by fluctuations in the speed of sound in the liquid, due to the presence of gas bubbles. The wavelength of this sound that is heard, determined by the size of the cup, and the frequency of sound depends on its velocity in the liquid. The presence of air bubbles in the liquid significantly reduces this speed. So the sound sounds more bass (lower frequency) with bubbles, and thinner (higher frequency)when there are no bubbles.