My money is on Pfizer. They have been quiet while Roche and Merck are making acquisitions lately. After the failed takeover of AZN, you know Pfizer is not going to sit around and do nothing.
I've been wondering that myself. Maybe Leo's not worried about ticking off Merck because he's already made the "momentous" deal that assures our future through a strategic alliance with one of Merck's competitors. Hmmm...