For all of Barry's genius he never could predict an emotional response. So he totally was blindsided by the tackle and had to steady himself so they both didn't fall over. After the initial moment of shock had passed, he was smiling and returning the hug.

"You're welcome."

Because really her actions telegraphed the "thank you" and didn't need to be said.

He gave her a tight squeeze of a hug as he felt a flood of emotions overwhelm him for a second or two. And his brain kept getting distracted by how good she smelled.

Pheromones his intellectual side told him.

Dude! Shut the fuck up and enjoy this! came the immediate emotional response.

He closed his eyes and went with the latte thought.