Sena wrote:
said...
Mouse enters, moves the card, second bucket slides down sealing both
exit holes....I've drawn a diagram because I've gone through this a
dozen times before on usenet and a lot of people struggle to
understand:

http://tinypic.com/view/?pic=161dwu9

I'm glad you drew the diagram because I was indeed struggling to
understand - although He Who Sits Opposite caught on immediately.
Don't you just love a smartraes.

Why two holes rather than just the one?

Because they rarely enter a deadend, rats are the same hence those traps
around factories which are basically just a piece of plastic drainpipe with
a slightly larger area inside for the bait....if it can see an exit it will
enter more readily.