Where Do They Learn These Things?

Today Lilly and I were putting together a puzzle and when we were finished she tried to pick it up without any pieces breaking apart. Some did and I hear her little voice say, "Shhh, damn." I paused. Did she really say what I think she said? In a very sweet, loving, non-judgmental voice I asked, "What did you say?" Lilly repeated, "Shhh, damn." I paused again. Do I let it go and hope she never says it again or do I casually suggest alternative ways to show frustration? Not wanting her to say damn at church or around other four year olds and their mothers, we talked about other things to say like "Oh goodness" or "Ah man". She thought it was a fun game and the subject was closed. Later, I told Kelly about what Lilly said and he was very quick to say she didn't get that from him. But, still, I have to wonder...