Hello.... I added a bit about in the bit about the bus.. If you get the DVD version of the film, and put on the commentary from the directors, they say that the blinking corpse was their mistake.. The actor playing the corpse blinked but they did not notice it until the final cut... If you do not have the DVD version, then this is a slip up! Also notice as the teacher goes to light the cooker (before she does) there is something sticking out of it! The directors say this is something to help the cooker explode later on in the scene and they didnt know this till the release neither!!
Of course he is not really dead; but in the film, he is SUPPOSED to be dead. Movies and slip-ups are about supposition. You wouldn't use a corpse to play the part of someone who died later in the film. This is a perfect slip-up. He is supposed to be dead.
PS: Post-mortem spasms/contractions would have died out by then.