By default duck duck go search engine uses safe search, so all your queries pass through safe search and you can't use the search effectively for some terms. In such case you should consider using query '!safeoff'.
This bang word will make sure that you have safe search off and you can now search for queries which are usually filtered during default safe search. Note that disabling safe search doesn't turn off the SSL search feature. So you're still secure and no cookies are placed on your browser by duck duck go.