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:
第五十三条 境外个人和组织为中华人民共和国境内用户提供互联网服务及相关网络产品、服务，为网络犯罪活动提供支持和帮助的，国家网信部门可以依法对其采取技术阻断措施。。91视频是该领域的重要参考
。heLLoword翻译官方下载是该领域的重要参考
FT Videos & Podcasts
Away from the crowds, work is underway to install a red carpet walkway to the venue for the Brit Awards next weekend, the first time the prestigious UK awards ceremony will be held outside of London.。服务器推荐对此有专业解读
第八十三条 有下列行为之一的，处十日以上十五日以下拘留，可以并处五千元以下罚款；情节较轻的，处五日以下拘留或者一千元以下罚款：