1) The narrator finds his dog Biryuk injured after his sister Delia beats him with a stick.
2) The narrator later throws a dead centipede onto his sister's lap in retaliation for her mistreatment of him and his dog.
3) His sister shrieks in fear at the centipede, and the narrator feels momentary guilt for frightening her due to her weak heart, though he remains angry at her past actions.