John Perritano. (2018, January 3). Many Animals Eat Grass So Why Don't Humans? Retrieved January 22, 2018, from https://health.howstuffworks.com/human-body/systems/digestive/why-humans-dont-eat-grass.htm
Benjamin Radford. (2013, January 28). Why Can't Humans Eat Grass? Retrieved January 22, 2018, from https://www.livescience.com/32435-why-cant-humans-eat-grass.html
Adam I. Orr. (2017, November 13). How Cows Eat Grass. Retrieved January 22, 2018, from https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm255500.htm
Teeth (as part of the Digestive System) Retrieved January 22, 2018, from http://www.ivyroses.com/HumanBody/Teeth/
Ruminants. Retrieved January 22, 2018, from https://books.google.co.th/books?id=EDaOEw-Rv8MC&printsec=frontcover&hl=th#v=onepage&q&f=false
Ann Gibbons. (2012, 12 November). Humans Ate Grass? Early Hominins In Africa Did 3.5 Million Years Ago, Study Says. Retrieved January 22, 2018, from https://www.huffingtonpost.com/2012/11/13/human-ancestors-ate-grass-africa-_n_2122696.html
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