This is what you experience when your head comes into contact with asphalt at around one metre per second or more (tested upto around 10m/s). On the surface it sounds like someone knocking together a pair of claves, but from the inside it sounds like someone dropping half a cow onto an upturned, fibre glass boat. This is usally almost instantly followed by the taste of blood and a smell like someone turning off a TV.

Generally unpleasant.