The snail is on a tightly stretched plastic sheet suspended over a light source - notice the small hole in the aluminum plate below.  The snail is exhibiting a localized (focal) withdrawal response to the radiant heat.  It is not withdrawing its whole body.  This behavioral response to heat is organized within neural circuits of the foot, but it can also be modified by the central nervous system of the snail.

Here the plastic sheet has been placed on a thick block of aluminum that is heated in a water bath (picture below).  This rearing response to heating is organized in the central nervous system of the snail.  Currently, we have eliminated the block of aluminum and place the plastic sheet directly on the surface of heated water.  This change has produced more reliable results.

 

This is the same rearing response as above, but now the plastic sheet is directly on the water.  You may now recognize that we use needlepoint loops to hold our plastic sheets tight; they work great!  The red color is produced by the red room lights that we often used during behavioral testing.  Snails are more active at night and are sensitive to light.   Red light doesn't affect their photoreceptors very much.

 

Live testing...the student (Mark, now accepted to Brown) is wearing magnifying lenses because we were measuring the reactivity of baby snails, which are pretty darn small.