Late-Day Trading

You're the analyst at Fidelity covering AMZN. You thought all the news on the stock was already out and fresh in the marketplace in the morning. The stock spiked $12 then faded to be up only $5 for the day. Kinda ho hum. But then at 2:37 EST, the stock spiked again. "What tf happened?", you wonder. This late-day trading was a surprise because as far as you can tell, there was no news. No nothing. But suddenly 6 million shares traded and you know you won't sleep well again until you know why.