Chik-Fil-A and KFC, hunker down. Shake Shack is releasing a limited run of chicken sandwiches in its three Brooklyn locations starting Tuesday. The ChickenShack, which costs $6.29, includes crispy all-natural chicken, lettuce, pickles and buttermilk herb mayo. It’s the first chicken sandwich offered by the trendy burger chain–but probably not the last. The experimental new offering could be an attempt by Shake Shack to spice up more than its menu.