Last night, Charlotte told me that her chest was making some knocking sound. I didn't know what she meant because I was in the washroom when she told me this and I ran out thinking what's wrong with her.
She pointed to her left chest and told me "mommy, here, got knock knock sound. why?". I still didn't know what she meant until she pulled my hand and put on her chest. I only realized that she was referring to her heart beat! Somehow, we got into some joke and play before that (it was bed time) and her heart beat was rising due to excitement.
I told her that it is her heart, and it is good sign that it is beating. It is not good when it stops, and she said "when stop means die ah?". I asked her to feel mine, but she didn't feel it (maybe I have to much fats that's why, ha!) and I asked her to put her ear on my chest instead. She said "yes, yes, got the knock knock sound too! like mine!".