Thread 1/2 tablespoon cranberries onto a small skewer; set aside. Place a small amount of crushed ice in a chilled martini glass. Add remaining tablespoon cranberries; set aside.
Fill a cocktail shaker with ice cubes. Add rum, cranberry liquid, and lime juice. Cover and shake vigorously to combine; strain into prepared glass. Garnish with skewered cranberries and serve immediately.