Corrected entry: If Dexter was working in Mondo Burger's kitchen before he got fired, wouldn't he have known they were putting chemicals in the burgers? In the scene where Ed and Dexter break into the kitchen and notice from the window where they're dripping the chemical in, it's the same prep area that Dexter worked in.
Corrected entry: When Ed "hears" the dog, it tells him there are four clowns in a broken down car. When we see the clowns in the cut away gag, there are 5. It is possible that the extra came out of the car (like a clown car) but not likley. It is also unlikely that Ed mis"heard" the dog, since that would defeat the gag. Finally, if it were a deliberate gag to have a fifth clown, there would be more emphasis on it.