I've had interviews where I've been asked to take a moderately obfuscated code sample, find out and describe to the interviewer what it does, and then find all the bugs in it.

To be honest, seeing about 200 lines that looked like this:

    typedef struct Abc {
        Abc *n;
        Abc *p;
        void *d;
    } Abc;

    Abc *foo(Abc *p, void *x)
    {
        Abc *n;

        n = malloc(sizeof(Abc*));
        n->p = NULL;
        n->n = p;
        n->d = x;
        p->p = n;
        return p;
    }

Note, there are at least 3 (edit: at least 4) bugs in the above code. None should be syntax errors.

Sorting it out was a bit of a challenge. I think the specific question that I was looking at deobfuscated into reading words and definitions in from the command line and maintaining them in a sorted list, then looking up the words and printing their definitions.

And I agree, it was a great interview question. I even had the ability to sit in front of the computer and test my fixes to make sure it worked.