Don't let cancer mess with your testis! Knowing your vas deferens from your epididymis makes a vast difference when checking your balls. Some folks mistake these scrotal structures for abnormal lumps or cancer during a testicular self-exam, so make sure you know the deferens -- ahem -- difference!
The epididymis, where sperm mature, sits atop your actual testis (the ball part) and feels like a soft swelling inside your scrotum. The rope-like vas deferens, which carries sperm from the testicle to the seminal vesicles and then the penis, leads out from the epididymis. Now you have an excuse to grab those gonads!