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:
这五年，河湖复苏见证生态蝶变。断流百年的京杭大运河连续4年全线水流贯通，断流二十六载的永定河碧波荡漾。越来越多的幸福河湖，正在成为百姓家门口的“诗和远方”。
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The president initially invited the women late Sunday, when he called to congratulate the men for their 2-1 overtime win over Canada. The women’s team was still in Milan, three days after also beating Canada 2-1 in overtime.
Фото: Pavel Kashaev / Globallookpress.com