"Sexual intercourse" and "bestiality" (sex with an animal) seem pretty clear - if your website displays images that a prosecutor believes involve minors engaged in sexual intercourse or bestiality, expect to be prosecuted. Which acts constitute "masturbation" or "sadistic or masochistic abuse" may be more difficult to define, because participants engaged in such activities tend to do so for a sexual purpose. Clearly a child could appear to be engaged in such activities without intending a sexual purpose. What a child intends by his or her actions is irrelevant, however, because Federal law prohibits "simulated" as well as actual acts. Many states also address this issue by prohibiting images of minors touching or displaying their bodies "for the purpose of sexual stimulation of the viewer."