Years ago when optical nice were a new thing, I pranked my co-worker in the IT department by taping a feather to the optical sensor and then taping the mouse right behind the power supply fan on his tower PC. Then I plugged in a second mouse and put it on his desk. The constant jitter of the mouse drove him bonkers. He replaced the desk mouse several times, went back to a ball mouse and even reimaged his PC (we used Ghost back then to image the company PCs in-situ). Every time he replaced his desk mouse I thought he'd see the rogue mouse, but he always did it "blind", tracing his cable back, pulling it out and fumbling with the replacement usb plug for 5 minutes, cursing USB ports. If he once pulled out the tower or crawled back there to look he'd have seen my ruse.