Well, I can assure you that the caterpillar was correct. It is, in fact, who are you, not whom are you.
Okay, so what is the difference between who and whom?
In my post about me vs. I, I briefly discussed subjects vs. objects. I = subject and me = object. In terms of who vs. whom, who = subject and whom = object.
Questions using who vs. whom:
- Who told you I pick my nose? (I don't pick it. I'm scratching an itch, thank you.)
- Who farted?
- Who farted on whom?
- Whom do you love? (Yes, Bo Diddley had it wrong.)
- Whom will Santa give big, fat, turd-sized coal to this year?
- Whom are you asking to the Sadie Hawkins dance (in his khaki pants)? (If you know that allusion, I owe you a cookie.)
- He told you I pick my nose.
- He farted.
- He farted on him.
- You love him.
- Santa will give big, fat, turd-sized coal to him this year
- You are asking him to the Sadie Hawkins dance.
Clauses using who vs. whom:
- Again, if you're talking about the subject of a clause, use who.
- Santa Claus, who brings fossilized poop to naughty children, actually loves to find out that you've been nice. (He goes not enjoy the smell of feces.)
- Ms. Wo, who acts like a total whackadoo, always finds new ways of amusing her students.
- Everyone laughs at the crazy teacher, who always leaves a lasting impression on her students.
- The pattern: In the clause, who is the subject. You could make it a sentence by replacing it with he/she.
- He brings fossilized poop.
- She acts like a total whackadoo.
- She always leaves a lasting impression.
- Santa Claus, whom children fear will bring them fossilized poop, would much prefer for you to be nice, not naughty; he really does not enjoy catching wind of your stinky stocking contents.
- Ms. Wo, whom students look at with raised eyebrows, always acts like a whackadoo just to see how students will react.
- Everyone laughs at the crazy teacher, whom students never forget.
- The pattern: In the clause, whom is the object. Another noun in the clause actually functions as the subject. You could write them as sentences by replacing the whom with him/her.
- Children fear him.
- Students look at her with raised eyebrows.
- Students will never forget her.
Whom do you love for telling you about who vs. whom?