The terms blackjack, cosh, and sap refer to any of several short, easily concealed club weapons consisting of a dense (often lead) weight attached to the end of a short shaft, used as a bludgeon. These weapons work by transferring kinetic energy to the dense core, via the handle, during the swing. When directed at the head, it works by concussing often also cutting the scalp in their classic design (solid lead striking head). This is meant to stun or knock out the subject, although head strikes have a high risk of causing a permanent, disabling brain injury or a fatality.