The color of money

On three consecutive days last month, about $150 went missing from schoolbags, which students must store in the hat room during recess. Harry was a victim - he lost $18 - and other students had cash and bus passes nicked. [...] On the fourth day, he placed a mouse trap with a $5 note attached in his school bag during recess. He had squirted the device's main bar and metal fittings with green food colouring, cutting a small hole in the note and securing it on the bait hook with sticky tape, so that the thief would have to wrestle with it, thereby setting off the spring and getting hit with the coloured bar. To his surprise, the thieves took the bait and - after he spread the word among classmates - a witch-hunt began. "I thought 'Oh my God, I might catch these guys'," Harry said. "Everybody was running around seeing who had green on their fingers." [source]