The exploding pie is a bomb that appears in the episode "Dying for Pie."
It looks just like a regular berry pie, with a golden brown crust and filling inside. It is actually a very powerful bomb which explodes when dropped. It will also explode in a few hours if eaten, killing whoever is unlucky enough to eat it.
Role in episode
It is Employee Brotherhood Day at the Krusty Krab, so Squidward buys a pie from a group of pirates for SpongeBob. However, the pirates inform him that they're actually bombs rather than pie. Squidward is left disappointed, saying that he was planning on buying one for somebody. Wanting a quick buck, the pirates lied by telling him that they are not really bombs, enticing him to buy one.
Once SpongeBob eats the pie, Squidward then realizes that it was actually a bomb and decides to make SpongeBob's last few hours of his life meaningful as a result.
However, it is revealed that SpongeBob did not eat the pie and it was in his pocket the whole time for him and Squidward to share. Unfortunately, he trips and the pie lands on Squidward's face, causing it to blow up in a nuclear-like explosion, destroying the Bikini Bottom in the process.
Despite the destructive power of the pie, it is apparently only lethal when eaten, as Squidward, Mr. Krabs and Spongebob were barely fazed when it blows up near them.