What I found is that written evidence for knocking on wood (and for the history of gesture as a whole) is remarkably sparse. In the Penguin Guide to Superstitions, folklorist Steve Roud offers a skeptical take on the provenance of knocking on wood due to the near total absence of written records about it:
（作者单位：北京大学考古文博学院）
，这一点在Line官方版本下载中也有详细论述
But the state government has told him he must hand it in and get a new one, as it was issued “in error”.，这一点在搜狗输入法下载中也有详细论述
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