Our brains are wired for problem solving and pattern recognition. In fact, it comes so naturally, we do it involuntarily. This Lands’ End mailer has “Lands End” embedded in the message (did you spot it?)–
The riddle is very simple but it does require brain activity. And this is what grabs the reader’s attention. Those few extra seconds the ad grabs means Lands’ End has significantly increased chances a potential shopper would end up using this promo. Tiny lift applied over a huge mailing list = big profits.
This example was from a direct mailer but there’s no reason why an e-tailer couldn’t use the tactic when promoting a sale via email.