Because there are certain lot orders of shares which are available at any moment as seen here
http://finance.yahoo.com/q/ecn?s=MMM+Order+Book
(not currently seen as the market is currently closed)
and there are bid and ask prices pretty much those are the prices that the seller/buyer is willing to pay for the stock and putting such a large move will pretty much buy all the stocks within their price range and thus even though the price may be $25... you bought all the shares for $24.30 all the way up to $26.20 thus increasing the value of the stock instantly towarRAB the $26.25 range but remeraber... he can't sell immediately because the buyers has an ask price of $24.90 so they won't be buying until they change their max order price.
Thats why Buffet, or other market movers, must make sure they invest into a company with a high volatility in volume... a stock that many people across the globe buy and sell on an hourly basis.
Make sense? Ask as many questions... Its review for me!