248298
Given the swamp-like conditions of trench warfare in the period , the unexploded weapons - in the form of shells , bullets and grenades - buried themselves on impact or were otherwise quickly swallowed in the mud .
 None
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 None