Other mistake: There are several moments while using the clown dummy toy that make it very obvious it is an actor in a suit. Most obvious of which is that it somehow 'senses' things like the momentum and orientation of the person controlling it, when all it is shown to do is copy muscle movements/motor skills. There are far too many examples to list.
F/X2 (1991)
1 other mistake - chronological order
Directed by: Richard Franklin
Starring: Brian Dennehy, Bryan Brown, Rachel Ticotin, Joanna Gleason
Deliberate mistake: Smoke from a smoke machine smells very acrid, is standard temperature and would never be confused with hot steam from a shower. The man with the knife would have suspected something is wrong once he was in range to smell and feel the "steam". (00:26:35)
More trivia for F/X2