It took the headline scanning algos several minutes to read Yellen's speech, which the kneejerk reaction was to deem as more hawkish than expected, before they stumbled on the key section we pointed out earlier, and which unleashed a surge of buying because it hinted at even more potential QE in the future (under a different Fed chair):

On the monetary policy side, future policymakers might choose to consider some additional tools that have been employed by other central banks, though adding them to our toolkit would require a very careful weighing of costs and benefits and, in some cases, could require legislation. For example, future policymakers may wish to explore the possibility of purchasing a broader range of assets.

This section catalyzed such an aggressive buying impulse that it required Stan Fischer's post-speech interview to pour cold water on the market's enthusiasm, saying "Yellen's comments are consistent with a possible September hike."  After all, as even Bullard admitted earlier, the Fed is perilously close to admitting stocks are in a bubble.