By now, you’ve probably heard about Idaho senator Larry Craig, who resigned last week after it was revealed that he’d been arrested — and pled guilty — to disorderly conduct. And you’ve no doubt also heard about his actions: He was caught engaging “in behavior commonly used to solicit sex, such as tapping his foot in the bathroom stall and touching the arresting officer’s foot with his own.”

But why do the police bust this sort of activity? In part, to prevent guys who aren’t interested in having public-bathroom-stall-sex from being propositioned there. Yet this weekend, Laura MacDonald wrote a fascinating op-ed piece in the New York Times pointing out that the toe-tapping gay-sex codes were designed specifically to be impenetrable to outsiders. Indeed, it’s a decades-old language, and it was first studied in a 1970 paper by Washington University researcher Laud Humphreys, entitled “Tearoom Trade: Impersonal Sex in Public Places.” As MacDonald notes …

In minute, choreographic detail, Mr. Humphreys (who died in 1988) illustrated that various signals — the foot tapping, the hand waving and the body positioning — are all parts of a delicate ritual of call and answer, an elaborate series of codes that require the proper response for the initiator to continue. Put simply, a straight man would be left alone after that first tap or cough or look went unanswered.

Why? The initiator does not want to be beaten up or arrested or chased by teenagers, so he engages in safeguards to ensure that any physical advance will be reciprocated. As Mr. Humphreys put it, “because of cautions built into the strategies of these encounters, no man need fear being molested in such facilities.”

The way MacDonald sees it, Craig is a victim of a communications-theory paradox. He got arrested for being a nuisance to others — yet the whole reason anyone uses the toe-tapping code is precisely to avoid being a nuisance to others.

I have to admit, I’m quite charmed by this defense of Craig. The problem, of course, is that it obscures the obvious fact that while the toe-tapping code is certainly discreet, it’s still illegal to have sex in bathroom stalls in the first place, no matter how discreetly. (It also elides the fact that Craig has spent his entire career inveighing against homosexuality — precisely the sort of political agitation that drives gay men into the closet, into untenable marriages, and thus, eventually, out into public bathrooms in pursuit of sex. You’d imagine the irony of this moral calculus would have occurred to him over the years!)

But back to the science. I was particularly fascinated to learn about Humphreys’ techniques. Since he couldn’t get his subjects’ permission, apparently he “tracked down names and addresses through license plate numbers, [and] interviewed the men in their homes in disguise and under false pretenses”. This is why “‘Tearoom Trade’ is now taught as a primary example of unethical social research”, as MacDonald notes. It also underscores the fact that we owe some of our most interesting social-psychology insights to research that wouldn’t be allowed any more because it’s too creepy — like the Milgram shock experiment. I’m not arguing in favor of unethical research, but it gets ya thinking.