Flea bite host, drink fill of blood, poop some when flea eat too much. Poop some blood, that is. Blood dries, look like dirt. Human think he clever to call it "flea dirt;" Flea call it "poor upbringing." Pooping on dinner never good table manners. Except in this case, Flea eating maître d.
Apparently flea dirt also source of nutrition for flea larvae, but Fleadirt not too good with kids, so Flea not know about that.
Flea head hurt from making meaning clear in writeup. Fleadirt noding on flea dirt asking for confusion.