I rewound a film canister too far and there's no longer a leader sticking out of opening. It had 10 exposures. I was taking it out to test something on the camera and was going to put it back in and fire 10 exposures with the lens cap on. If I'm SOL'd, it's no huge deal as it was expired B&W film anyway, but it would be nice if I could still use the rest of the exposures. How can I avoid doing this in the future?