click food word experiment subjects The messenger role pet friend or companion as. cleaner/recycler of nature assistant teacher medicine traditional Chinese medicine,horn,ant,bezoars(牛黄)， leech(水蛭/蚂蟥)，venom(蛇蝎等的)毒液，bile(动物等的) 胆汁， Unit 4,Book 4food medicine friend or companion experiment subjects messenger assistant teacher pet cleaner/recycler of nature Unit 4, Book 4 meat, pork, beef, mutton, milk, chicken, venison（鹿肉）, . guinea pig (also called cavy 小白鼠), monkey, often used for biological studies, experiment in space, etc. . pigeon, dog, etc. for delivering messages, or acting as guide for the blind walk, save one’s life, talk to each other, . Dogs are considered man’s best friend. Other pets such as parrots, cats, dogs, etc. have been considered good companions of human beings for many years . earthworm, vultures, eats away toxic dead bodies of animals, etc. terriers (小猎犬) for helping digging for small game in hunting; dogs for leading the blind, detecting drugs or dangerous objects such as bombs or explosives in airport luggage. Sheepdogs are extensively used as assistants for farmers to manage the sheep in New Zealand and Australia . bionics (仿生学) , human beings learn to produce new machines and devices based on the analogy of the animals, e.g., helicopters, submarines, etc. . traditional Chinese medicine, horn, ant, bezoars (牛黄), leech (水蛭/蚂蟥), venom（蛇蝎等的）毒液, bile（动物等的） 胆汁, . The role as . click the word