Were I a bot, I could easily up the volume to get that by accident.
Make it 4 kittens, and you're at a .8% success rate.
Make it "kitten, dog, pony" in that order and you're at a .2% success rate.
Your typical "type in this word" gives bots a far lower success rate than any of these options.
However the user friendliness of it might make it a winner.
Cheers,
Ben
PS There is still no defence to a bot that displays what it got to the user of a porn site, who has to enter the answer to see the next dirty picture.