We had rats — I wanted to catch them without harming them. Things were going well but it came down to one recalcitrant holdout who had learned all of my tricks, and I had to resort to some extreme measures to try to catch it. (All these rats were released unharmed.) Music is from my album Frost Flowers: http://caseyconnor.org/?p=disco
If you’re trying to decipher the notes in the schematic, the reference to the “arduino” and the “Pi” are referring to the case where the NPN/solenoid is being triggered by a logic signal from those devices, instead of a 555 timer. Sorry for the confusion there.