The Texas Chainsaw Massacre is a very odd, vile little film, but it's arresting viewing, it has to be said (though the many spin-offs and sequels have definitely followed the trend of diminishing returns.) The original was low budget, around $300,000, which meant that safety on-set suffered, which lead to things like the scene at the beginning where the nutter slashes himself with a razor actually happening. That blood is completely real, since the film-makers just couldn't afford fake blood after spending so much money on the farmhouse and actors. However, the most insane fact is probably the fact they used a real running chainsaw in all the scenes involving one. Yes, including the bit where it is being held by the actor who cannot see through his mask centimeters away from the lead actress's face. The real mishap came at the end of the film where Leatherface is running with the chainsaw. Gunnar Hansen, the actor playing Leatherface, slipped in the mud and sent the chainsaw flying into the air. Jensen fell to the floor, the still-running chainsaw landing insanely close to his face. It's hard to believe that the making of a movie could actually be more violent than the film itself, but the Texas Chainsaw Massacre has proved us all wrong.
