Why do some people gag when someone is vomiting?

Why is it that when a person vomits, it causes others to vomit — even when they don't have an illness causing it? Is this something triggered by the brain or is it something that happens by reflex (survival instinct) for someone to vomit since, perhaps, what the first person was eating may affect the second who vomits as well?


Where can I find the birth control sponge and what’s the efficacy rate?

1) I've always used condoms combined with a sponge for birth control. That worked well because if anything happened with the condom, there was always a backup — it made me feel safer. Then I get to New York, I go into three drug stores, and none of them have sponges. Now what? I don't want to rely on just condoms, I don't want to take pills because the whole hormone thing is rather frightening, and a doctor said that diaphragms make you more prone to get urinary tract infections, which I get frequently. So what am I supposed to do? What's up with this total absence of sponges?

2) In exploring other forms of contraception, what is the reliability rate of the "sponge"?