The "halo cloud" was just an optical illusion caused by sunlight hitting a cloud at just the right Angle.

“光环云”是由阳光以恰到好处的角度触及云层而引起的一种光学错觉。

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Mirror tic Tac Toe by Peleg Design is a rad little optical illusion board game with half o's and X's that only are complete when put in play.

佩莱格设计的镜面井字游戏是一个超赞的迷你视觉幻想棋盘游戏，半o半x的棋子只有在玩起来放在棋盘上的时候才完整。

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In a second optical illusion, the Ponzo illusion, the volunteers were shown two identically sized circles superimposed onto the image of a tunnel.

第二个是蓬佐错觉，志愿者可以看见在一条隧道的图像上有两个大小一模一样的圆。

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Since human depth perception relies on calculating the difference between the angle of view coming to each eye, the result is a 3-D optical illusion.

FORBES: Adventures in the Third Dimension

An ardent young heiress named Sophie (Lisa Henni) tells him approvingly, almost worshipfully, that when he looks he truly sees, yet Sophie can't see that the man she's falling in love with is an optical illusion, a pair of eyes reporting to a brain that's unconnected to a heart.

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May stressed the new "effect" was not a hologram, calling it "an optical illusion of sorts".

BBC: Freddie Mercury