2. The Texas Chainsaw Massacre (1974)
The Texas Chainsaw Massacre was one of the first major films to say 'based on a true story.' Because it was the first, many people believe that there really was a horrible cannibalistic family quietly nibbling on people whilst their crazy son chopped up the next meal for them. For a start it says these events took place on 18th August 1973... filming finished on 14th August 1973. The film is actually loosely based on real life serial killer Ed Gein of whom numerous films have taken inspiration from including Alfred Hitchcock's Psycho. At that point in Texas there were no records of massacres involving chainsaws having ever occurred and I really hope there hasn't been any since. TXCM is quite a scary film and it's now a horror classic but thankfully none of it happened in real life so don't worry!