Who knows why people do what they do. Some look, some bow their head, I am sure some are not really paying attention. I know all this, because there are times when I am watching what other people are doing and not paying good enough attention at the elevation of the host. I get sidetracked in my own mind and it wanders sometimes. I usually catch myself pretty quickly when I realize I am not showing enough respect and am quick to apologize to our Lord

I, for the most part, do say “My Lord and My God” at the elevation of The host. When I remember to. Sometimes I just gaze and contemplate the mystery of The True presence.
As for the ringing of the bell… When I was in RCIA, our parish Deacon told us (I don’t remember exactly what he said) that when the Jewish priests use to go into the temple for some ritual or ceremony or something that they use to wear bells on legs so that when they walked, the bells would ring. That would signify that The presence of God was there. So, I am guessing he meant that when we ring the bell, it means “The presence of The Lord is here” Now, I do not remember what our Deacon told us word for word, so if this is wrong in any part, it is probably because remembered something differently from what I was told.