I have no idea whether the price offered was a good one, but the reason that both the rumors of talks, then the dissolution of talks, could cause the stock pric

I have no idea whether the price offered was a good one, but the reason that both the rumors of talks, then the dissolution of talks, could cause the stock price to rise is pretty simple: 1) Rumors circulate of a pending acquisition. Obviously that acquisition will have to happen at a premium to the current price or it won't happen, so that's a signal that if you buy at today's price, you can sell in the acquisition and make a profit. People start buying on that rumor, causing the price to rise. 2) Reports subsequently surface that a $55B offer, which would have been a premium from the original price, was rejected and that $70B was sought. People think "well maybe the real clearing price is something like $65B" -- and that's higher than today's price, so people buy at today's price in hope of making a profit if/when that transaction eventually takes place. The price therefore rises again. Again, no idea what the price "should" be today, but it's not illogical that the price could rise both on the rumor and on the end of the rumor (especially when, as here, the explanation for the end was the (possibly self-serving) "the price wasn't high enough!").