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“String cheats” are small time crooks who attach fishing line or sticky tape to a banknote they’ve inserted in a vending machine so they can drag it back out after they’ve got the goods. But Mars, better known for its chocolate bars, says it has invented a vending machine that can defeat string cheats (WO 02/44985). The trick is to shine polarised light onto the path the banknote follows to the cash box inside the vending machine. Mars has discovered that even the thinnest string or tape following the note into the machine changes the polarisation slightly. This can be detected and used to trigger an alarm. At the same time, a mini guillotine comes down to sever the line.