I couldn't understand the meaning of "little twist" in this sentence:
Prime Wardrobe offers a little twist, however: The more you keep...
Amazon today launched Prime Wardrobe, a service like Trunk Club and other online retailers that lets you order clothes and return them free if they don’t live up to your expectations. Prime Wardrobe offers a little twist, however: The more you keep, the more you save. Keep four items in your box and get 10 percent off. Save five or more and receive 20 percent off. Boxes are resealable and come with a shipping label.
All the meanings that I've found for the word "twist" sound weird in the context of this sentence. What is the correct meaning of "little twist" here?