The Incredible Shrinking Man

The Incredible Shrinking Man is a movie based on the book by Richard Matheson titled The Shrinking Man. In the movie, a man named Scott Carey is exposed to some type of dust cloud (generally assumed to be radioactive) and the result is that he begins to slowly shrink. It is considered one of the better shrinking movies because the script is considered intelligent and the science is a little more believable.

The Incredible Shrinking Man was added to the National Film Registry in 2009.

Tropes used in The Incredible Shrinking Man include:

Bittersweet Ending/Downer Ending: Mileage will vary on which one this is. Scott's voice-over monologue at the end has him accepting the inevitable and reaffirming that no matter how small he is, he will still matter in this universe. That doesn't change the fact that he will eventually shrink to atomic size or worse, that his wife assumes that their cat had eaten him.
Cats Are Mean: You just knew that the cat was going to try to eat poor Scott when he got small enough.
Did Not Do the Research: Spiders that live in webs don't normally leave them to hunt.
Giant Spider: Technically, the spider is normal sized, it's Scott that's small, but from his POV, it is giant.
Hollywood Science: Due to the Square-Cube Law but may have been mildly averted; see below.
Incredible Shrinking Man: The trope namer, of course.
Magic Pants: Completely averted. Scott's physical body gets smaller while his clothes don't. As a result, he is forced to wear children's clothes, doll clothes and the rags from his doll clothes.
Mouse World: From the scenes in the dollhouse to being chased by the cat, and finally being trapped in the cellar. In the cellar, this is the epitome of the Mouse World. Scott is forced to eat crumbs from a stale cake, live inside a match box and fight off a spider.
Narrating the Present
Square-Cube Law: Quite possibly averted because Scott slowly shrinks, thus giving his body a chance to adapt.