ever wonder how an old-school Christmas tree "flasher bulb" works? check out this microscope video.
yes, it's one of those bulbs with the red tip. you plug it into a string of bulbs and it flashes the whole string because they're connected in series. 
the metal contact that moves ever so slightly is actually a bimetallic strip -- a sandwich of two different types of metals.
when the filament heats up, the metals expand at different rates which causes the contact to curve away from one of the terminals, which breaks the circuit. the filament turns off and won't turn back on until the temperature falls again.
it's an electromechanical relaxation oscillator!
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