He was taking elbows from the bottom, used one arm to wipe the blood off his brow dripping in to his eye, he let his sub defense down, arm wide open. Silva slips on a finisher first controlling the arm, then silva throws that leg over. BAM BAM BAM, the power of submissions.
If I remember the multiple angles he tried to get out with his free arm, then two real taps as he was fading into the darkness. 'Sonnen didn't tap' proclaimers need to grow up, go watch the fight again. Go watch all the previous non-taps Sonnen has had over his career, a few are probably very similar to Silva's.