It takes two. One to change the bulb, and the other to kick the switch.
or
One; she designs the bulb to crawl up the wall, unscrew the old one, and screw itself in.
or
She couldn't control her pupils.
or
It saw the ginger snap.
or
They're both plastic and little boys turn them on.
or
One has claws at the end of its paws and one has a pause at the end of its clause
or