Well, you don't really PLAN to eat it, but you're saying it's so clean you COULD eat off it if food should happen to fall. (In reality, you'd probabaly throw it out. It's just an expression.)
By the way, do you know about the "three-second rule"? If food falls on the floor (of your own kitchen) and it's on the floor less than three seconds, it's still edible. This applies to things like biscuits, not scrambled eggs. It's not a real rule of course, but you may see it on a tv show sometime:
- Food drops
- "Ooops!"
- Bends down to pick it up and put it back on the plate
- "Oh well, three-second rule."
- (Audience laughs.)