So I was rewatching the end of Sandcastles in the Sand cause it's amazing and fantastic, and I noticed something.

Ted said in Swarley (after Robin found out that Ted's 'shy vulnerability' look was fake) "Oh yeah and you biting your lower lip, shyly looking away and thrusting your chest out is natural?". I think Robin sort of does that at the end of Sandcastles before she started making out with Barney... It wasn't exactly what Ted described, but look closely at Robin and you can tell that she was thinking about it and she knew exactly what she was going to do. She had this adorable flirty mannerism going on! Take a look! The part I'm talking about is just really quick from 0:14 to 0:16... you'll see though.