The first time the bell sound occurred I was the only one that heard it. I was away from the group, in the bathroom when I heard it. The second time it occurred, approx and hour or so later, another one of the 4 of us heard it too but she didn't want to say she heard it. I could tell she heard it simply based off of her body language, facial expression, the direction she looked in, etc. I believe the only reason she heard it was because I quickly brought it to everyone's attention, as it was happening, and had to interrupt everyone to bring attention to it.