243. Extending and Returning Greetings
Kriyas Shema 2:16
If a person is in the middle of a section of Shema, he may pause in order to greet someone he is afraid of, like a king or a despot. He may return the greeting of one whom he is required to honor, like his father or teacher.
Kriyas Shema 2:17
The breaks between the sections of Shema are: between the first and second brachos; between the second bracha and Shema; between the first and second paragraphs of Shema; between the second and third paragraphs of Shema. At these breaks, one may greet a person whom he is required to honor and he may reply to any person’s greetings. However, between the third paragraph of Shema and “Emes v’yatziv” is considered the middle of a section. Accordingly, one may only interrupt to greet one whom he fears, or to respond to one whom he is required to honor.