What is the role of an immigration judge in determining whether an alien's testimony has the ring of truth?

An immigration judge alone is in a position to observe an alien's tone and demeanor, to explore inconsistencies in testimony, and to apply workable and consistent standards in the evaluation of testimonial evidence. He is, by virtue of his acquired skill, uniquely qualified to decide whether an alien's testimony has about it the ring of truth. The courts of appeals should be far less confident of their ability to make such important, but often subtle, determinations.

Sarvia-Quintanilla v. INS, 767 F.2d 1387, 1395 (9th Cir.1985).