Gotcha!

Fett is now certain that the sound he heard when he punched Atton earlier wasn't his imagination...so, after a little bit of time forcing Atton into painful dodges, Fett throws another punch...at the same spot he nailed Atton with the earlier, rib-cracking punch.

And yes, there might just be a smug grin on his face as he plans it to give away what he intends to do.