This is waaay over my "institutional investor knowledge base", but from what I understand, many sophisticated investors have a way of "buying" insurance against violent stock price swings (options) that most small fry investors lack or simply don't use.
I seem to remember a link posted here a while back that took me to site that listed "options" held by Anavex's institutional holders. I'm only 40% sure about that being the case though, so take that with a whole bowl of salt please.
It would be interesting to have some of the most sophisticated investors dissect that info (if it truly exists) .