Quote Originally Posted by Gerald C Koch View Post
When you first wind off 3 exposures to get past the leader watch to see if the rewind knob turns. If it does then the film is loaded correctly. If not then gently test to see if you can turn the knob as if to rewind. if you cannot turn it more than say a turn or so without tension then the film is loaded correctly. This should become a habit whenever you load film.
After having a couple of blank rolls, this has become my standard operating procedure when shooting 35mm. Some Canon's also have a rotating eyeball (for lack of a better term) to show that film is actually moving, which comes in handy if you forget to test the rewind.

Similarly, I once double-exposed 3 of the 4 4x5 shots I developed (not *that* long ago), and the other one was totally blank due to a mix-up in my numbering scheme. Took me at least an hour to shoot those 4 frames, plus an hour to load/unload and develop them. At least they weren't chromes, is all I could tell myself.