This is a handheld Doppler unit, and it's designed to let you listen to the blood rushing around inside your head. Why would you want to do that? Well, detecting how regular the bloodflow in your head is is how one detects a concussion, so having this on the sidelines of a football field or in a medics pack on a battlefield would obviously be very helpful. Also, it'll totally blow your stoner friends' minds. Whoa, dude, that's what the inside of my head sounds like!