Shivvay has always managed to make her nervous and awkward whenever he has the intense look that kinda undresses her just by the way he looks at her. Tripping frankly at that scene would have been natural since they were already in a dimly lit room and all alone. This is after all the man, who not long ago, attempted 2 unsuccessful first nights with this woman. So she knows very well what is going on in that head of his when he looks at her like that. There is no guess work needed here, he has spelt it out very plainly in the recent past.
Heck!! I would be nervous enough to trip in her place if I were her, just walking past him, trying to maintain my composure while I knew he was itching to reach out and grab.
Shivvay expecting her to fall and prepared for it was a given because he meant to unnerve her. I have noticed that he enjoys the effect he has on her only because she is such a tomboy and a strong woman. He loves that she gets weak around him, it's like a high for him ... lol