7430
Recent studies have discovered that gecko ' s extraordinary climbing ability comes from a remarkable design of nature with nanoscale beta - keratin elastic hairs on their feet and toes , which collectively generate sufficiently strong van der Waals force to hold the animal onto an opposing surface while at the same time disengaging at will .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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