Is this one of those spot the difference things? Is Raynor's hair style a bit different or something? Or a star? Give me a minute... edit: I see it! There's something hanging out of his mouth in the bottom picture. What do I win?
That will be the new Terran unit in Heart of the Swarm: Marines have a new tier three ability called "Aspect of the Kitty", where their body suits transform into cats. This gives them a big speed bonus, but capable of close range combat only, and vulnerable to rubber mice and balls of string. While in kitty-form, they can cast "Meow", that confers them with a cuteness buff causing enemy units to occasionally miss in combat.