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:
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It is focussed on West Antarctica, home to 30-40% of the global population of Emperor penguins. The animals are amongst the most threatened in the world.，更多细节参见搜狗输入法2026
Жители Санкт-Петербурга устроили «крысогон»17:52
Раскрыты подробности похищения ребенка в Смоленске09:27