1. If someone is praying together with the cantor, when he reaches Kedushah, he should say the entire Kedushah word for word together with the cantor. He should intend to finish the blessings of “Hakeil Hakadosh” and “Shome’a Tefillah” together with the cantor. He should also coordinate that when the cantor reaches “Modim”, he is also either at “Modim” or at “Hatov Shimcha Ulecha Na’eh Lehodos” so that he also bows together with the congregation. (Mishne Berurah 109)
2. If the cantor reaches Modim and the one praying is in the middle of a blessing, he should bow together with the congregation. However, if he is at the beginning or end of a blessing, he should not bow down, as one may not bow at the beginning or end of any blessing apart from the first blessing of the Amidah and Modim. (ibid)
