To give you an idea of what we mean, here's a chart of PFE from our platform: The chart shows us, in red, whenever dark pool short selling occurs. As you can see, a fairly substantial amount of shorting took place in the days surrounding the deal announcement. These are probably owners of AGN who want to hedge out their newfound price correlation with PFE - quite understandable. But, by the end of November, over a week after the announcement, only 65.5M shares of PFE were held short - not much more than normal. Even then, the arbitrage spread was ~ 20%, so why weren't people buying AGN and shorting PFE to capture that huge spread? Where were the usual arbitrageurs? Apparently, the deal was still perceived as too risky. Four months later... Look at what's happened to PFE short interest ( NASDAQ ): Up by