Dear Reader,

Kudos to you and your boyfriend for sharing your observations and experience — what an opportunity to learn more about how our bodies work.

The cool, subtle vibration you described and witnessed may have been due to testicular circulation. Veins and arteries allow the blood flow to run through the entire scrotum.

If your boyfriend's testicular movements were even more pronounced, then you can thank his cremaster muscle. It gently bungees the testicles to whatever part of the neighborhood they need to hang comfortably in. Another muscle, the dartos muscle, helps move the testicles up and down inside the scrotum. Together, they enable, as Kramer would say, "the boys," to dance.

Testicles are temperature sensitive sperm factories. Sperm need to be kept at a certain temperature to be happy and healthy. When the "boys" get cold, they snuggle up and get warm. Feeling stuffy, they can hang lower to get cool. Just before orgasm, the cremaster and the dartos muscle work as a team to bring the testicles into lock and (un)load position.

Here's another learning activity you and your boyfriend can try that can also get the "boys" to dance just for you. Touch the upper inner portion of your boyfriend's thigh. His testicles will move in the direction away from where your hand is touching. This response is known as the cremasteric reflex, which is a safety maneuver that the testicles perform to stay out of harm's way. When the threat is over, the testicles will come back to a position with which they feel temperature friendly and safe.

Alice!