Oven Logic: Marge's cake was so hard it broke a bullet-proof glass.
Previously On: Parodied. As part of another allusion to "24", this episode starts with a narrator treating it as a sequel to a previous episode. The narrator even mistakenly calls the cartoon "24" before correcting himself.
Serious Business: the bake sale and an attempt to disrupt it is taken by the hall monitors as a 24-style threat. Justified Trope on the bake sale (see As You Know above) and the stink bomb because it is something obscenely powerful.