How the crabs crawling
螃蟹的八条腿是长在甲壳的两侧，并且腿 关节只能向下弯曲。当爬行时，必须先用一侧腿的趾尖抓地，再用另一侧腿伸直起来，把身体向一侧推过去，所以螃蟹只能横着走
Crab's eight legs are long on both sides of the carapace and legs and joints can only bend down. When crawling, you must first side of the leg with toe grip, and then the other side leg straight up the side of the body to push the past, so crabs can only go sideways.
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