Heights.

I believe that when God made the penis he created it with a device that senses heights to warn us. As soon as I get really high up and close to the edge its triggered and makes my junk tingle. I can only assume God made this device in the wiener for the soul purpose that the penis and balls are obviously the most important organ on the body, of course I"ll listen. The balls converse with the penis about the correct time to trigger the alarm.

Balls "Hey penis me and my twin were talking and we are like 3/4 up the Superman Tower of Power, should trip the height alarm?"
Penis "No not yet."

Balls "Penis we are getting pretty high up now almost to the top, how about the alarm?"
Penis "Good call testicles, let's trip the alarm."