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Say you’re riding home on the Metro, minding your own business, when you just so happen to notice a guy repositioning himself to better rub his erection against a stranger’s back. You’ve just become a witness to a sexual assault. Now what do you do? Commenter m the great posed the question after a recent column: “If I see someone being mistreated like that in public, what could I possibly do to help?”

Excellent question.

Yesterday, I spoke with Lauren Taylor, lead instructor of Defend Yourself, a D.C.-based self-defense organization that shops around “skills for stopping harassment, abuse, and assault.” Taylor, who has over 25 years of experience teaching self-defense, offers some tips for bystanders who find themselves witnesses to harassment or assault, and want to do something about it:

* Look out for number one. “Always think about your own safety first,” Taylor says. “Look at who’s around who could back you up if necessary. If you’re inside, say at a bar or social event, figure out where the doors are.”

* Speak to the victim. “When you’re thinking about intervening, address the person you think is being targeted,” Taylor says. “Say to her, ‘Are you OK?’ Or, ‘Can I do anything?’ Or, ‘Do you want to come with me?’ This won’t necessarily solve the situation, but it will let her know that there are other options. It will let her know that people are seeing what’s happening, and it lets the harasser know the same thing. There are witnesses, and it’s not going to go unnoticed.”

* Make a scene. “For example, you could draw attention to it by saying something like, ‘This guy is putting his hands all over her!’ Or, ‘This guy is harassing her!’ and that could draw enough attention to the situation that the harasser would cut it out,” Taylor says. “Airing any of these things, and making them more visible, will ultimately make them better.”

“Now, the harasser may respond by saying, ‘Who are you? This has nothing to do with you! She doesn’t mind!,'” Taylor says. “But you still have transformed what’s going on, and possibly made it safer. The harasser talking back doesn’t mean it didn’t work.”

* Even if the victim doesn’t ask for help, you can still do something. “Like with everything, it totally depends on the situation,” Taylor says. “Especially if it’s a partner thing, you may hear the victim respond, ‘Oh, I’m okay, go away.’ But I still think it makes a difference that it was noticed and recognized.”

“There’s no prescription for anything in self-defense,” Taylor says. “It’s the options that are empowering, not the solution. I can’t promise that any one thing will work, but I can give you the things to try, whether the target asks you for help, or whether you say, ‘this looks unacceptable, and I’m going to check it out.'”