杏吧原创

Alton, Hampshire, UK

Grinning or baring the teeth is usually a sign of aggression in animals, so at what point did it become advantageous for humans to use this to signal friendship or mirth?

Veronica Haines,

Llanelli, Carmarthenshire, UK

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How does water become 鈥渟tale鈥�?

Bob Yelland

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