According to shortanalytics, there has not been a lot of short activity in this stock ... until today, when half the trading volume was short. Which suggests that perhaps most of the short positions are really hedges against long positions. In fact, most of the biotechs which advanced strongly today were heavily shorted. In CELG, which made a new high today, 70% of the volume was short. The exception would be GILD, which had very low short volume. I have never found a strong relationship between short volume and prices. I would be happier if there were more real shorts in this stock, vs those who buy a few puts hoping for another AFFY.