In this question, it mentions Amaterasu (Amaterasu-omikami) retreated into her cave after Susanoo (Susano'o) did a bunch of things to her. It does not elaborate further on this, save for the flayed horse thrown at her weaving girls.
How else did Susanoo terrorize Amaterasu?
Initially, Susanoo ruled the Takama no Hara (High Celestial Plain) with his sister Amaterasu but from the very beginning, Susanoo caused trouble by destroying forests and mountains and killing local inhabitants down on earth. For this reason he was banished from heaven.
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Full of exuberant joy at having won his challenge with his sister, Susanoo went on another wild rampage in celebration. Once again, trees were destroyed and so too many rice-fields. Then, to add insult to injury, in a rather tasteless joke Susanoo flayed a divine horse and threw it through the roof of the palace where Amaterasu was quietly weaving.
