Emphasizing Auxiliary Verbs 

Usually,auxiliary verbs like do,be and have are contracted.

But when they are the most important word in a sentence,they are said in the full form.

A. I don't have to work today

B. yes, you do have to work, and right now.

____

A. That's a mean dog.

B.Yes, it is a mean dog, but not as mean as mine.