kinda true split second... well... close friends i will tell them, eh zao geng liao... if acquaintance then normally just shut up...
Yup, it is also courtesy to remind her. This reminds me of an incident during a meeting. My female colleague was presenting a slide at a meeting at HP when her bra-strap fastener gave way. Nobody noticed that, but I just happened to see it at that moment. Hence, I stood up and offered to take over, so that she could go to the restroom. Then after the meeting, she thanked me and joked with me that I was so 'observant'.