My conjecture/speculation on what happened to PIP today, fwiw (and I'm just guessing):
SIGA closed up 10% on normal volume due to continuing bullishness from longtime SIGA fans plus the effects of a few analysts and dawning recognition that its stock is underpriced (regardless of appeal verdict), generally, plus the appeal's looking good. I.e. just more of the trend we've seen over past couple weeks.
So why is PIP up 10% on huge volume today? I'm guessing an algorithm recognized that PIP and SIGA ought to be joined at the hip due to Parson's verdict. But the two stocks have diverged more and more lately without any explicit factor to justify it. So the algorithm bought the bejesus out of PIP to try to profit from the apparent illogic, and other algorithms spotted this activity and tried to capitalize on the same disparity. This accounts for the enormous volume and sharp climb by PIP today.
By contrast, I think the previous PIP upward baby steps over the past couple of weeks, all at low volume, were just the result of SIGA investors hedging as they loaded up more SIGA shares.