So go to dogpile (a search engine results aggregator, it appears), and enter "gun" or anything with it ("gun control," "guns of navarone," and more"). You'll get this response, unless you have a cookie set with dogpile from a previous iteration:

You've entered a Web search term that is likely to contain adult content.

Would you like to:
View Unfiltered Dogpile Web results with Adult Content.
View Filtered Dogpile Web results with NO Adult Content.
Filtered Results only include Web results from partners that provide such results.

Warning!!! If you are under 18 or live in a place that viewing adult content is prohibited, please revise your search.

Your Search Filter is currently moderate.

Of course, "sex discrimination" and anything else with "sex" will give you the same response; "breast cancer," however, doesn't, even though other "breast" queries do. "Murder," "making meth," and lots of other queries do not give this response.

Now I don't want to suggest that the filter is particularly onerous. In fact, in some ways it's the opposite: It lets your kids avoid it just by clicking on "View Unfiltered Dogpile Web results with Adult Content," or, at most by following the Preferences link in the search results (if you've set a preference that prevents the above warning from coming up). Dogpile even prominently tells the user, with every batch of search results, "Your urrent preferences are set to filter results for this type of keyword and/or search. Click here to change your preferences." Oh, and the first result in the "heavy" filtering mode for sex? "Free Sexy Webcam Striptease Videos" (which seems to be exactly what the name suggests).

On the other hand, how can we know? I'm not aware of whether dogpile actually filters out much gun stuff using its filter. The no filtering query returns 65 results while the heavy filtering query returns 62 results; I haven't compared them closely, partly because the most obvious difference is in the order of results — for instance, heavy filtering gives the Wikipedia entry for "gun" as #1 and the official site for "gun the game" as #2, and no filtering reverses that order.

But dogpile's description of its filtering hardly instills confidence: It describes the filter as being "designed to filter out sexually explicit material from your results." If that's all dogpile is doing, there seems to be little reason to warn readers about searches involving "gun." Something is happening under the hood, and we don't know what it is — an inherent problem with all filtering software, but even more of a problem when one part of the site tells you one thing about the filter ("designed to filter out sexually explicit material") and another part tells you another ("gun" is "a Web search term that is likely to contain adult content"). Doesn't make this search engine look particularly trustworthy, it seems to me.

Thanks to Peter Buxtun for the pointer.

UPDATE: Some readers have suggested that "gun" could be flagged because it's occasionally used as a slang term for "penis." But "peter" and "johnson" are probably more commonly used as slang terms for penis than "gun," and they rightly aren't barred. If every term that has a primary meaning far removed from "penis," but has sometimes been used as slang for "penis," were filtered, that would be a very long list.