Old World bird having a very long tail that jerks up and down as it walks
wagtail详细解释
wag.tail n.（名词）Any of various chiefly Old World birds of the family Motacillidae, having a slender body with a long tail that constantly wags.鹡鸰，亟灶巢鸟：主要在西半球的一种鹡鸰科鸟，具有瘦长的身体和不断摆动的尾巴
