Fun with trains
There is an industrial railway spur near where I used to live, with an unmanned level crossing going over a moderately busy road. About 50 metres down from the crossing are the sensors that the train triggers as it rolls over them (slowly - this was just a spur line remember). The sensors were placed, one on each rail, and when the train went over them it completed a circuit, setting off the bells and lights at the level crossing, stopping the cars. We discovered that you could complete this circuit with any conducting material that spanned the two sensors. So we grabbed a metal fencepost and laid it across the rails, touching the sensors. Bingo. The lights began flashing, the bells began ringing and traffic came to a stop. We just sat in the woods and watched traffic build up on both sides of the crossing, waiting for the non-existent train to cross.
(ring-finger is also a verb, Wed 4 May 2005, 20:18, Reply)