How does stretto build intensity near the end of a fugue?

In a musical fugue, stretto builds intensity by overlapping the entries of the subject.1

Normally, the subject is stated in one voice before another voice enters with the answer. In a stretto, however, the subject begins in one part and then proceeds in another before the first statement has finished. By compressing these entries so that they occur in closer succession, the composer creates a sense of urgency and density, which is why this technique is frequently employed near the end of a fugue to build toward a climax.1