It’s apparent that Google believes that its search algorithms are capable of determining the searcher’s intent. It is also obvious that Google filters out explicit image content, regardless of user settings. If you don’t believe me, just search for a few sex acts in the image search without any filtering and witness the effectiveness of the over-riding search restrictions.
This leaves the researcher wondering what words are on the “restricted” list. With all the euphemisms for sex acts it is easy to see that searches not related to sex acts might be restricted by Google’s all-knowing, all-seeing, algorithm.