Whilst doing a bit of research on anniversary clocks I came across a few intresting articles on a Haller clock that through a combination of bad design and wrong use of plastics can literally self destruct on your mantle piece and can cause injury, they where eventually withdrawn from the market, if you have one call bomb disposal
The danger comes from the fact that the mainspring for this 400 day clock is wound onto nylon spools that over time become brittle and can fail at any time releasing all the energy from a reverse wound spring this as earned them the nick name "The german time Bomb"
http://erkelzaar.tsudao.com/models/ultra/german-tb.htm
http://www.anniversaryclockidentification.com/pages/sh-gbt.pdf