Make sure one is a match!
or
One. You don't believe me do you? I've got photos! See that big blob? Well, just squint your eyes a bit. . . .
or
One is a blood-sucking parasite, the other is an insect.
or
He was a baaaaaaaaad driver.
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1,000,001: One to change the bulb and 1,000,000 to rebuild civilization to the point where they need light bulbs again.
or
Put it in a glass with some ice cream and root beer.
or
A traffic jam.
or