It could do bizarre things including destroy the computer or make zebras fly out of the USB port.

That reminds me of a post I read in comp.std.c a long time ago:

> Now what happens if, oh, you do THIS:
>
> foo()
> {
> int x;
>
> x=10;
> if (x) free (&x);
> }
>
> I know that malloc uses heap space and that the local variables take up the
> stack, so what happens? &x is NOT null so it will try to free it, so what
> happens?

Shit happens. Exactly what shit happens depends on the implementation.
Since this is in the realm of undefined behavior a conforming implementation
is allowed to launch a pre-emptive strike against Iraq.

That was posted by Stanley Friesen on 1990-12-19, which is unfortunately older than what Google Groups has archived, so I can't give you a link to it.