NEW YORK ( TheStreet) -- IntercontinentalExchange ( ICE)'s announcement Thursday that it would acquire NYSE Group ( NYX) sparked strong moves in the three other public-traded US exchanges, though the scenario implied by those moves invites a great deal of skepticism. Shares of Nasdaq OMX Group ( NDAQ) rose 3.53% to close at $26.11, while shares of CBOE Holdings ( CBOE) gained 3.96% to $30.68. Are investors betting they'll be acquired? Who do they think will do the acquiring? Richard Repetto, analyst at Sandler O'Neill, was left shaking his head. "No one knows. Some other exchange from overseas. I don't know. Maybe Nasdaq tries to buy CBOE. It's just these merger arb guys that just don't know the space very well and the whole space goes up on stuff like this," he said. Even if Nasdaq and CBOE do get acquired, it isn't at all clear they should be worth more than they were as of Wednesday's close. Deals take many forms, and market responses are difficult to predict. That unpredictability was clearly in evidence Thursday. NYSE shares opened 38% higher at $33.27, slightly above the agreed-upon price of $33.12 per share, before drifting slightly lower throughout the day to close at $32.25. Shares of ICE, meanwhile, opened 5.5% higher but quickly dropped, spending much of the morning and early afternoon in negative territory. They recovered in the final two and a half hours of trading to close at $130.10, a gain of 1.40%. CME Group ( CME), meanwhile, started out higher, but spent most of the day below where they closed on Wednesday. Shares closed Thursday down 2.34% to $51.40. The market's apparent conclusion is that CME faces a much stronger threat from a combined NYSE and ICE. But analysts appeared to express a healthy amount of skepticism about Thursday's deal. Barclays Capital's Roger Freeman, for example, wondered where the planned cost savings would come from. "Can you just talk a little bit more about where all these additional opportunities are? ICE, your margins are already at very high levels. Does this imply that Project 14 (an NYSE cost-cutting plan) missed a lot of additional opportunities?" Freeman asked on the conference call following the deal's announcement.