Corrected entry: Zoidberg said here that he has three hearts, but in the Roswell episode he said he had four.
Corrected entry: Fry has lives in the 30th Century for three years and Freedom Day is an annual thing, so how come he's only just discovered it?
Correction: Fry is an idiot. Maybe he was watching TV all day on the previous two Freedom Days, or is just dumb enough to have forgotten.
Correction: Zoidberg tells the US soldiers that they can "keep it (the heart they pull out during the autopsy), I've got three more", so he did have four, but lost one for good.