More evidence to refute Cardiovascular Risk, page-47

Ok... Shorting is actually a slightly complicated process.

A large institution (in this case UBS) needs to hold the actual equities. A client of UBS can then 'borrow' the stock from UBS (paying a small premium to do so). They can then give the stock back to UBS when it suits them. If the share price falls, then the stock they give back to UBS can be purchased at a 'discounted rate', hence the profiteering from a drop in the share price.

Now in Acrux's case, it appears the bump in share price on Thursday last week caused some short sellers to panic, essentially causing them to 'buy back' and then self-perpetuated the share price rise.

It's similar to a margin call scenario, however just in reverse.