1) A company (ex: RXI) approaches Big Money investors (no, not Big Pharma)
2) Company arranges to offer them "X" number of shares at a fixed price below the current PPS
3) Big Money immediately sells (shorts) the "X" number of shares they agreed to buy later (driving down the price - though they don't really care what happens to the price)
4) Big Money buys their shares at the agreed-upon fixed price, covering their short position