Two. One to take out the bulb and drop it, and the other to try and sell it before it crashes.
or
but I'd never seen herbivore [her before]
or
One who knows how to play the saxophone, but doesn't!
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One in 3,000,000 has a chance of becoming a human being.
or
Emmental...it's very hol(e)y...
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Anything you like, he can't hear you.
or
A fence.
or
He made an illegal ewe turn.
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An udder failure.
or
Twenty. One to hold the bulb, two to turn the ladder, and 17 to be on the guest list.
or