When Fry is nailing the "1" to the "X days since the last accident" sign, he puts the nail in the top center of the "1" and the angle shifts to the back of the sign. When the angle shifts back to the front, the nail is not in the top center of the "1" it's to the right of it and through Fry's hand.
Many thousand years ago the people from Osiris four visited the Egyptians and learned from them, among other things, how to space-travel. If they didn't know that before, how they got to ancient Egypt in the first place?