What is Bom Bom Butz?

A Game; The act of very gently and repeatedly tapping your forehead against a baby's or toddler's forehead and saying "Bom, Bom, Butz" in order to engage the baby and get him/her to giggle. This is very much a Jewish activity as the words are Yiddish. Bom is pronounced "Bomb" and Butz rhymes with puts.