They are very similar to normal Krabby Patties from the exterior, but upon biting into one, they are clearly spray-painted to look like Krabby Patties, and the food itself is an unknown gray substance from a patty-making machine.
Role in episode
They were made from a gray substance that comes out of a machine, heated and cooked in a furnace, and finally spray-painted to look like a regular Krabby Patty. Seeing the process sickens SpongeBob and Mr. Krabs and eventually, the latter reveals the interior of the patty to all of the Krabby O'Monday's customers. At first, the customers enjoy the patties, but as soon as they see what is inside, most of them flee the restaurant in horror.
- People would notice the flavor of the patty changed dramatically, especially if they were regular customers of the Krusty Krab, and since the gray substance was used for all of the components of the Krabby Patty (bun, patty, toppings, etc.) It’s possible it was highly processed enough to taste good.
- Its also possible they failed to notice because the interior's atmosphere was distracting them.