Two: One to screw you out of a fee, and the other to send you to a store where they ran out of bulbs weeks ago.
or
The cow that jumped over the moon
or
One is a blood-sucking parasite, the other is an insect.
or
1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
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Because it might crack up!
or