I've seen this movement before on KIM (Kimberly Diamonds) just before a takeover was announced by GEM Diamonds. It could be a cunning ploy to hammer down the share price through short selling to lower the VWAP for a low-ball takeover bid. The bigger players can be real bastards doing this as it screws over the retail players big time. If anyone is interested have a look at the share price history of KIM just before the takeover.