That`s no moon...

"That's no moon!" phrase (movie quote)used to describe an imminent encounter with something that is much more deadly than previously assumed. 
Ex: "Did you say he shrugged off the axe blow and the lightning bolt bounced off his breastplate? That's no moon...!" [JB3]
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Addendum: Spoken by Obi-Wan Kenobi (Sir Alec Guinness) in Star Wars: Episode IV: A New Hope, when he realizes that he's looking at the first Imperial Death Star. [JB3]