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On May 22 , 1856 , in the United States Congress , Representative Preston Brooks attacked Senator Charles Sumner with his walking cane in retaliation for a speech given by Sumner two days earlier .
 Preston Brooks, Charles Sumner, Sumner
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Preston Brooks, Charles Sumner, Sumner