Things that happen with various local stations: (1) lousy reception--intermittent or constantly (2) "late" returning to the show after commercial break (3) network graphics over part of the screen (4) local announcements continuously with or without broken aspect ratio
(all of which make watching a show on hulu preferable to watching a local broadcast, which isn't to say the shows aren't garbage [shrugs], but as long as the garbage is free...)
That's almost true. Pixelation happens when the signal strength drops enough. (Don't tell me you've never seen that.) And if it drops some more, then there's nothing.