Billing Displacement: Top-billed Jennifer O'Neill doesn't appear until the 37 minute mark and is more of a supporting character to Stephen Lack's character. Michael Ironside is billed fifth despite arguably playing the most memorable character of the film.
Writing by the Seat of Your Pants: The first film was written like this, which was forced upon Cronenberg because of the way the production had to be structured due to financing reasons. There was virtually no pre-production, so he had to start shooting with an unfinished script. He would write in the morning, and film the rest of the day, mostly out of order. On top of that, they often had to drive around at random, looking for places to shoot scenes. So literally everything about Scanners was done by the seat of their pants. He talks about it at some length in Cronenberg on Cronenberg.