I'm not being sarcastic. They actually look like black dots.
A period is actually two pixels on my computer, at least (15" 1440x900), so smaller. Get really close to your monitor. You'll see squares. Those are pixels. When one dies, it'll go black.
If you have a single-colored pixel, that's a stuck pixel, not a dead one. Those can be fixed, dead ones cannot.
Honestly? They look annoying! They really bug a lot of people, and when screens have fewer than five of them, people have to live with them because Apple won't replace a screen with less.
It's just a really tiny dead area of screen that never changes from black. I guess it throws off the "illusion of depth and motion" on a computer monitor.