Because they put little things at the bottom of the screen throughout the episode. Kinda like that old "Pop-Up Video" from VH-1. Sometimes it's just reminders of things about the story arc. "The song Charlie is humming is his one hit wonder." Or "These numbers have been shown throughout the series in blah blah."

Sometimes there's been behind the scenes mentions. Like how they're really standing on this beach in Oahu or something. Just little trivia things, nothing spectacular.