Printer that shoots javelins
I once worked on a computer impact printer that printed on green bar paper 132 columns wide. The printing mechanism was a bank of 132 electrically actuated hammers. The hammers impacted a the paper against an inked ribbon onto the printer font. The font characters were cast on a bar about 40 inches long. This bar rode in bearings linked to a powerful electric motor that made the bar reciprocate back and forth very rapidly so the printer could print hundreds of lines a minute. There was an access door on the side of the printer so the bar could be removed for maintenance. Occasionally the link would break and if the timing was right it would strike the access door so hard it would fly open. The story was going around that someone left the access door open, the link broke and the print bar embedded itself in the side of the mainframe computer nearby.