Imagine Sour Foods Like Lemons
If this still hasn’t got you salivating, then you can imagine sour foods like lemons or sour sweets. You could also try smelling them if you happen to have them in your kitchen. This service says that they do not recommend that you bite or scrape your cheeks.
The reason for this is that the cells in your saliva sample that will be analyzed by the company are your white blood cells and not the epithelial cells from your cheeks. These can get mixed in if you bite or scrape your cheeks.