I am still quite the incurable romantic and there was a good deal of Mr. Knightley and Emma glancing at each other throughout the ball. From Ch 38:

".....Whenever she caught his eye, she forced him to smile..."

And, quite often it is fun to ponder what is not said but subtly implied. For instance:

When was the last time that Mr. Knightley and Emma danced together? Could it have been years or never? Again from Ch 38:

"..... with what natural grace, he must have danced...." It appears that Emma never had danced with him or even seen him dance at all!

Now, to take that one step further: Since dancing was just about the ONLY appropriate activity where men and women could actually touch each other in public, methinks it impossible that both Mr. Knightley AND Emma both could not fail to get a thrill out of that! Mr. Knightley because in his hands was no teenager but a mature woman dressed to the nines, and Emma, to be thrilled both at Mr. Knightley's dancing skill AND with his youthful, upright carriage. (for his age)