Sexual arousal though they are generally considered secondary in role to the other three. Erotic stimuli which can result in sexual arousal can include conversation, reading, films or images, or a smell or setting, any of which can generate erotic thoughts and memories in a person. Given the right context, these may lead to the person desiring physical contact, including kissing, cuddling, and petting of an erogenous zone. This may in turn make the person desire direct sexual stimulation of the breasts, nipples, buttocks and/or genitals, and further sexual activity. Erotic stimuli may originate from a source unrelated to the object of
Sexual arousal also accounts for their high individual variation, is the "preparation hypothesis". This hypothesis suggests that, provided there is enough of an increase in vaginal blood flow for vaginal lubrication to occur in a sexual context, the magnitude of arousal need not be consistent. That is, the hypothesis is that vaginal lubrication can take place as a protective mechanism even in a non-preferred sexual situation, such as when sexual activity is non-consensual. Other researchers argue that since the research is done on people who volunteer to be studied, the observed levels of category specificity may not represent the population, that there