When you're cold, your scrotum pulls closer to your body to keep the sperm warm so they won't die. When you're warm, the scrotum(scrotum means bag for those unsavvy folks) retracts(or sags) so that the sperm don't get overheated.
All my friends are skeletons,
dulcimers and chariots
prayers to God, oh prayers to God
Was I sleeping all this time?
Was my shadow ever mine?Wintersleep-Danse Macabre