When meeting, especially with social superiors, Cambodians traditionally Som Pas while saying Choum Reap Sur (Hello). When leaving, they will again Som Pas while saying Choum Reap Lir (Goodbye), usually as a display of respect. If you are greeted in this way, it would be impolite not to return a Som Pas as it would be tantamount to us rejecting an offered handshake in our culture.