He answers a reporter's question, then very quickly calls on the next journalist without taking a breath. Check out how Spicer rushes to the next question over and over, in the video above.
This serves a few purposes for Spicer. First, it fends off the loud cacophony of questions that can erupt during any gap in his answers. Second, he controls who's asking the questions; that means he can avoid particularly probing or adversarial journalists if he chooses. Third, and perhaps most important, it prevents the journalist who asked the original question from asking deeper follow-ups. Spicer is telling them: That was my answer, and I'm not adding more.