h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Scuba Diving Law No. 1 - Look, don't touch.

Don't complain to me .. I'm not a diver. I just heard that somewhere ...

yes, "Take Pictures, Leave Only Bubbles"

That sums it up rather well. It's a very good rule of thumb to follow at first, anyway. After you've gained some knowledge about the habitat, you'll discover the exceptions. For instance, I knew one old man in Hawaii who decided he didn't want to work any more, so he began gathering shells on his dives. He knew where the tides deposited them, so he just gathered them, polished them, and strung them on fishing line for necklaces. He was a pretty good source of information for us, and he always volunteered to keep an eye on our cars (breaking into the cars of someone stepping out for a dive is easy prey, since you know they won't be in a position to do anything about it for nearly an hour), so as a courtesy, everyone I dove with took turns buying necklaces off him. Mine hangs on my rear-view mirror still.

One of the guys I used to dive with discovered that there was a certain type of urchin that could be found in those waters with a very attractive shell. With a few inquiries, he also discovered that if he found one and cleaned it up and polished it a bit, he could get a decent amount of money for it. From then on, whenever we dove, whether for rubbernecking or for spear-fishing or lobster hunting (two more times when it's perfectly acceptable to touch ), he always kept his eye out for them.

Actually "look don't touch" was the first law of being a child. At least according to my parents. The first Law of SCUBA diving as anyone who has been certified could tell you is "never hold your breath." Lung overexpansion injuries are hard to survive.

What's "lung overexpansion"?

This bit from the article sums it up pretty well:

"As you ascend rapidly, the air in your lungs also expands rapidly. If you hold your breath, your lungs will explode."

Of course, you don't have to ascend rapidly for this to happen... just as long as you ascend, and hold your breath all the way, you'll do this to yourself. And there's also the chance of squeezing air out of your alveoli and directly into your bloodstream, which will give you an embolism.