It's worse than that though. Most of the algos see the PR, and then look for arbitrage opportunities created by it, but also use the stock price fluctuations as

It's worse than that though. Most of the algos see the PR, and then look for arbitrage opportunities created by it, but also use the stock price fluctuations as a signal for sentiment. All you need is one algo to stupidly misjudge sentiment and you create a thundering herd.