When used with a degree of safety and considerable artistry, blood in wrestling acts as a symbol for violence as opposed to genuine violence. In short, it's a work; the shallow cut is opened over the forehead, to ensure a photogenic and not inconsiderable pour - and to minimise the risk of bleeding out. To sustain the drama, an opponent can re-open the wound, designed to seal quickly, with a worked punch.
Yes, this is entertainment - but as the Great Muta discovered in legendary fashion, the hazards are real. In a notorious 1992 match opposite Hiroshi Hase, Muta entered with crimson face paint and, after a blade job masquerading as a crowbar spot went awry, left with a particularly gruesome crimson mask. As the camera first captured the visual, Muta slumped to his knees - at which point the red stuff poured all over the canvas to form a pool. Blood coated his entire body, and that of his opponent. It was the wrestling tape trader's Faces of Death.
And thus the Muta Scale - the barometer against which all future blade jobs were judged - was born. Even through the grainy VHS transfer, the gore is revolting - though not entirely as definitive as the official title suggests.
Many bemoan the lack of blood in modern wrestling, which is somewhat understandable, much as a certain drama is missing.
But the scope for life-threatening injury is frighteningly high...