You might have seen melting movie film, because the small frames needed such intense light to fill a screen that if you didn't keep the film moving (if it got stuck) most projectors would melt the film.
Originally Posted by winger
Doesn't happen much with 35mm.
But, I had a Bell & Howell Slide Cube projector which melted one of my favorite slides. The darn thing was engineered only for square corner cardboard mounts and had real trouble feeding the later round-corner mounts. But it ran hotter than any other projector.
Still, I'd rather show for 20 seconds - a real slide on a real screen... and have that experience. Than miss out because I was worried about ruining the slide.