Final answer:
It is unclear which rock sizes snakes prefer when given equal numbers of different sized rocks, as there is no specific research linking rock size preference with snake behavior in the provided information. The preference, if any, would likely be based on their survival needs such as camouflage and thermoregulation.
Step-by-step explanation:
The question concerns the rock size preference of snakes when offered different sizes - thin, medium, and thick rocks. The question does not directly link to an established study or behavioral observation of snakes choosing rocks based on their size. In the context of the provided information about snakes, which mainly focuses on their eating habits and physical characteristics, there is no relevant data that would suggest a preference for a particular rock size by snakes. Since snakes are carnivorous and swallow their prey whole, the size and type of rock they might choose to interact with would more plausibly depend on how it relates to their hunting and hiding habits rather than a simple preference.
Without specific research on the topic, one can only conjecture that snakes would choose rocks that best suit their needs for camouflage, thermoregulation, and security - factors more crucial for survival than a preference based on rock size alone. If there is a preference, it likely has a biological or behavioral rationale rather than an arbitrary choice.