Toddler Swearing

I have no idea what it means, but for the past few months Kaylee's been saying, "no kooka" (or however one might spell it?) in a semi-whisper. She usually says it to the cats or me, and it's apparently not nice because if I say it back to her she gets very mad and hits the floor or table or whatever is close. So it's apparently some sort of toddler bad word or something. Of course I find it funny, but I tell her it's not nice to say that and try not to laugh at her. :)