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:
有被侵害人的，公安机关应当将决定书送达被侵害人。
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Жители Санкт-Петербурга устроили «крысогон»17:52。搜狗输入法2026是该领域的重要参考
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