Final answer:
Mary used sensory checks to ensure she got the best shellfish, such as tapping the crabs to see if they stayed closed and tapping the clams to see if they stayed closed.
Step-by-step explanation:
Mary used several sensory checks to ensure she got the best shellfish. One of the checks she used was tapping on the crabs to see if they stayed closed. If they stayed closed, it indicated that the crabs were still alive and likely fresh. Another check she used was tapping on the clams to see if they stayed closed. If they stayed closed, it meant that the clams were still alive and safe to consume.