All right so let's say you and the little woman want to spice things up in the ol' boudoir and are getting bored with vanilla sex. Adding chocolate sauce helped but you can only lick up so much of it before your teeth rot out. After a little discussion (communication is important), you decide that you want to try out some light bondage and discipline. Maybe some master and slave play.
Put down the vibrating nipple clamps for a minute, kids, cause you need to learn about safe words first.
We all know that no sometimes means yes. Well when you're down on all fours getting the handle of a bullwhip shoved three inches up your rectum with a stiletto heel in the small of your back, no usually means yes. Stop means more and ouch means oh baby, do that again! The problem here is obviously how to tell "Stop, that hurts" from "Stop, no seriously that really hurts."
There's a fine line between dominant and abusive. Abusive isn't disco.
So before you zip up that gimp mask, choose a safe word. A safe word is a word that wouldn't come up in casual conversation when licking your mistress's shoe. Words like Pepsi, bookshelf, or Peter Griffin's favorite, banana. If you're not feeling very creative you can even use safe word. When you stop screaming in pleasure and start screaming in pain, it's time to use it. Doms, I know you don't like being told what to do, but give a guy a break and respect the safe word. This is supposed to be fun for both of you and if he's going to come crawling back like a slavering dog, he's got to trust you. Like a slavering dog.
But wait, there's more! It doesn't have to be that simple. There can be multiple levels of safe word, for those occasions when you don't want her to untie you, just stop squeezing your balls so hard. The green safe word means everything's okay, and can be used as a double check when the dom isn't sure if she's taking things too far. The yellow safe word means "ease up a little, but don't stop." The red safe word means "All right, that's it, cut the ropes, take off the mousetraps, and get whatever that is out of my ass. I'm done." If anyone knows if the traffic light analogy can be extended to the protected green arrow, /msg me with your phone number, 'cause baby I like your style.
At the very least, the safe word can help keep things fun and not painful or scary. At the most extreme it can prevent permanent damage and even an accidental death. Asphyxiation isn't just autoerotic, you know. Just don't overuse it. If you stop the beatings every time you need to scratch your nose, you're A) probably missing the point and B) crying "wolf." On the other hand don't be afraid to use it when you need to. Mistress might be a little disappointed with your weak, quivering flesh but she doesn't want to break her toy either.
And speaking of asphyxiation, you can't speak when you're asphyxiating. Or being gagged, strangled, hung, drowned, or having your head encased in plaster of paris breathing with straws up your nose. So for those uncomfortable moments when you've found yourself mute, the safe word can be a gesture. Two taps, a pinch, or drawing your finger across your throat can all be effective. Otherwise you might want to hold onto some object while everything is going well and drop it when you want to stop.
But wait! There's still more! Safe words have application outside the bedroom, and I'm not just talking about that back shelf of the library nobody ever goes into. The safe word can be used any time acting is involved to increase realism, whether it's a training simulation or literally acting on a stage. You don't want anybody to really drown during lifeguard training, deliciously ironic though that would be. Similarly when Osric says "Holy crap! Hamlet just nailed Laertes a good one!", it's helpful to know whether he just flubbed his lines or the actor is really missing a chunk of artery. An episode of The Boondocks featured a rapper performing his hit song I Just Been Shot and was consequently unable to convince the audience he had, in fact, just been shot.
So keep it fun, kids, keep it safe. Remember to establish a safe word whenever you're performing.