1) When a person makes a bracha, he is required to eat or drink some of the food immediately. (S.A. 167:6) One may not speak until some of the food is swallowed. (M.B. 35)
2) If one did speak (about something unnecessary to the eating) before taking the first bite his bracha is not valid and a second bracha is required. (S.A.)
3) The Mishnah Berurah writes that if one first put some food in his mouth, started chewing it, and then spoke before swallowing it it is questionable whether the bracha is valid. It seems that his conclusion is that b’dieved the bracha is valid. However, it is important for people to avoid this issue and only speak after swallowing some of the food. (See V’Zos Habracha page 14)
4) The poskim explain that one should not make an interruption even if one does not recite any words. For example, if one wishes to instruct a family member to be quiet, he should not say “shh” or “nu” after reciting the bracha before swallowing some of the food. (See V’Zos Habracha page 16 and V’Sein Bracha page 46)
5) Similarly, one should not hum a tune after the bracha before eating the food. (Minchas Yitzchak 7:9 and Shevet Halevi 5:16. See, however, Halichos Chaim page 62 for a more lenient view) This is very common on Shabbos after the bracha of Hamotzi before eating the challah, one should not hum a tune. If one did hum a tune another bracha is not recited. (Shevet Halevi ibid.)
Halachablog 