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:
儘管這份工作對身心都有高度要求，麥肯齊表示，沒有任何事能比得上他所經歷的那些令人難以置信的時刻，以及為環境研究作出貢獻的滿足感。
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Within Python job picks only (61% extraction rate). Custom/DIY = asyncio tasks, no external queue
Овечкин продлил безголевую серию в составе Вашингтона09:40
Some economists say that more Dutch women need to work full time