It is a reaction and Jenny smiles gleefully at it. His face has turned some wonderful shades of red and as for other reactions, well, close proximity does reveal those as well.

Her thoughts radiate something about winning and about love and about how much better this Bart is from the solemn impostor that was there moments ago. There's also something about payback in there. Oh, yes. Definitely something about payback.

One hand still firmly on his crotch, Jenny places the other on his shoulder and uses it to push him down on to the booth seat. She crawls on top of him to pin him in place, hand finally leaving that part of him.