The Secret Patty is almost similar to the original Krabby Patty, except that the sandwich is completely dark orange and levitates. When swallowed, it turns people into Krabby Patty creatures. This same effect happens to anyone who eats any portion of a Krabby Patty creature, which apparently causes a secret patty to be consumed by said victim as well.
The Secret Patty can apparently also affect computerized objects such as Karen. The only known manner to reverse the secret patties' effects is for the victim to consume chum, which causes the victim to spit out the Secret Patty and return to normal.
Role in episode
After he hears that one of his customers wants something new to eat, Mr. Krabs hires Sandy to create a new-and-improved version of the Krabby Patty. At first, the Secret Patty turns out to be a success, but at the end of the day, it is revealed to have a terrible side-effect. Whenever someone eats it, they become mutated into Krabby Patty creatures.
During the chaos, SpongeBob learns that the only cure for the patty's effect is raw chum and saves the day. Once everyone is cured, Mr. Krabs and Sandy both learned their lesson and decided to never sell the Secret Patty again. When everyone agreed that they all miss the original Krabby Patty, they leave the mess of patties in the Chum Bucket.
According to the storyboard, the Secret Patties were originally going to be purple.
SpongeBob is the only character in the episode who is not affected by the patty's effects since he never ate one.