Peripherals such as keyboards, mice, printers and monitors all have cables that connect them to the main computer and/or power sources. If one of these cords is unplugged, the likelihood of the individual checking the cord is low. The greater likelihood is that they will believe the device is no longer working.
Disconnecting the power cord is generally the easiest issue (though surprisingly not always) for the average user to self diagnose and correct. Better options include the USB cords that connect the peripherals to the main computer. Unplug at the device and not the computer. Most assume it is the computer connection that is at fault and will check it. Many others will simply keep trying to diagnose the peripheral using software.
Prank variation: Unplug the mouse of a close individual’s mouse over lunch. Plug in either a wired or wireless mouse to the individual’s computer. Watch for their return. When they access their computer, use your mouse to open programs and watch their eyes grow wide. They will believe there is a ghost in their machine.
* Wireless variation: check if there is a wireless receiver plugged into a USB port. Treat this as you would a cord.