I'm posting this ex-post facto because I had to run just before the market opened.
Here's what I was watching:
OPK agreed to buy BRLI at a pretty large premium, and OPK was down about 5% in the pre-mkt ala ALXN a month earlier. OPK IV isn't as cheap as ALXN is generally, with back months at 50% compared to ALXN's around 35%. OPK appeared to open at 60% IV and it got more than paid as the stock cratered thoughout the day.
VZ was down about 2.5% on a downgrade in the pre-mkt, and that low vol name makes a gap like that attractive to play.