Inferior Alveolar Nerve and Mandibular Block

A 35-year-old patient requires extraction of the lower left first molar. The dentist plans to administer an inferior alveolar nerve block. The structure marked **A** in the diagram represents the nerve that must be anesthetized to achieve successful block of all ipsilateral mandibular teeth and lower lip sensation. Which of the following is the most appropriate clinical endpoint to confirm successful anesthesia of the structure marked **A**?