Each student or small group of students can watch the eating process if the food is mixed with water, painted onto a microscope slide or other piece of transparent glass or plastic. A thicker paste, applied with the fingers or a spatula can also be used. As snails eat, students can see the snail's radula scrape the food off the glass. Tooth marks should be visible in the cornstarch left on the glass. Have students count the strokes of the radula per minute.
Snails eat both cornmeal and cornstarch.
If time limitations force you to choose between the two, use cornstarch. The courser texture of the cornmeal gives less detail. However, having students compare the marks left in the two substances encourages more detailed observation than simply having them look at one or the other. This lesson can be done as a demonstration, and the class can view the tooth marks in the cornstarch via an overhead projector, but much detail is missed this way. To test snail reactions to a variety of textures, tastes and smells.