Two balls moving across each other can be perceived either as streaming through or bouncing off of each other. Presentation of a 'collision' sound timed near the crossover of the balls reverses this dominance by facilitating the perception of balls' bouncing. Change volume to check the effect of sound.
Sekuler, R., Sekuler, A. B., & Lau, R. (1997). Sound alters visual motion perception. Nature, 385(6614), 308.