Hammer of Lightning - Kaminari no Tsuchi

...Thus, it is believed that thunder is said to take the navel, and this is why people would make children wear belly bands as soon as distant thunder began to rumble. It is also said that thunder axes, thunder balls, and thunder hammers rained down during thunderstorms. On closer inspection, most of these are relics from the Stone Age, and many of them are stone axes. ...

*Some of the terminology explanations that mention "Thunder Hammer" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…それで雷はへそをとるといって，遠雷が鳴りだすとすぐ子どもに腹がけをさせたりする習慣をつくり出したものと思われる。雷雨の際に雷の斧とか雷の玉，雷の槌とかが降ったといわれることもある。よく調べてみると，その多くは石器時代の遺物で，石斧類のものが多い。…

※「雷の槌」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報