Using the popular pop rock candy, an individual places it in their mouth and proceeds to conduct oral sex on another individual, whether it be on the penis, vagina, anus, or nipples. While the pop rocks explode in the giver's mouth due to the reaction with the saliva, this explosive sensation is transferred on to the "sensitivities" of the receiver, a "hummmmm" type feeling is received.
A common example of a pop rock hummer would be during a blow job. The girl puts some pop rocks in her mouth and once the pop rocks start "popping", she sucks the guy off. The same tingling sensation she receives in her mouth is transferred to the guys penis. This works even better the other way around when a girl gets eaten out because the pop rocks not only react with the saliva, they also react with the delectable juices of the vagina.