Thanks to extensive practice with the sling, you gain the following benefits:

• Increase your Dexterity score by 1, to a maximum of 20.
• You gain proficiency with slings.
• With tinker's tools and one hour of work, you can drill holes in up to 20 sling bullets. This special ammunition "whistles" in flight.
• When you use the Attack action and attack with a sling, you can use a bonus action to attack with the same sling once again.
• When you use the Attack action and attack with a sling which is loaded with a "whistling bullet", the target must succeed on a Wisdom saving throw or become frightened of you until the end of its next turn. A creature must make this saving throw at most once per combat encounter. Constructs, Undead, deafened creatures, or creatures immune to being frightened automatically suceed on the save.