formication
  蟻走感
  for·mi·ca·tion /ˌfɔrməˈkeʃən/ 名詞
  For·mi·ca·tion n.  Med. A sensation resembling that made by the creeping of ants on the skin.
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  formication
       n : hallucinated sensation that insects or snakes are crawling
           over the skin; a common side-effect of extensive use of
           cocaine or amphetamines