According to General Order 2, what should a sentry do at their post?

A sentry is trained to maintain a high level of vigilance and professionalism while on duty, as outlined in General Order 2. Walking in a military manner and staying alert are essential behaviors expected from a sentry to ensure they can effectively fulfill their responsibilities. This includes being attentive to their surroundings, ready to react to any potential security threats or observations that align with their duty. A sentry's posture and alertness not only reflect military discipline but are critical for maintaining security and safety in their assigned area.

The other options do not align with the principles set forth in military orders. For example, leaving the post when tired could compromise security and is not permitted. Focusing solely on personal safety undermines the sentry's duty to protect others and their post. Engaging with civilians might distract from their primary responsibilities, which could lead to lapses in security. Thus, walking in a military manner and staying alert is the correct response expected from a sentry.