宗教问题：西方人说谎时为什么食指和中指双指交叉然后把手放到身后？

两指交叉代表十字架
比出十字架代表寻求上帝保佑
所以这是说谎时为不遭报应，于是比出的一个手势

※十字架原是罗马帝国处死犯人的刑具，但因为耶稣在十字架上受死之后，十字架被赋予了新的意义，代表着上帝对世人的爱与救赎，是神圣不可侵犯的标志。

The earliest use of the gesture had two people crossing their index fingers to form a cross. To use the gesture is considered an excuse of telling of a white lie by children. By extension, a similar belief is that crossing one's fingers invalidates a promise being made.

To cross one's fingers is a hand gesture commonly used to wish for luck. Occasionally it is interpreted as an attempt to implore God for protection.[1] The gesture is referred to by the common expressions "cross your fingers", "keep your fingers crossed", or just "fingers crossed". The act of crossing one's fingers mainly belongs to Christianity. The earliest use of the gesture had two people crossing their index fingers to form a cross. To use the gesture is considered an excuse of telling of a white lie by children.[2] By extension, a similar belief is that crossing one's fingers invalidates a promise being made.[3]

参考自Google维基百科&百度百科