9987
This has led to formulation of the " venom optimization hypothesis " ( Wigger et al . ( 2002 ) Toxicon 40 , 749 - 752 ) , also known as " venom metering " , which postulates that venom is metabolically expensive and therefore used frugally through behavioral control .
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Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
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