A curly arrow, or curved arrow, is the symbol used in reaction mechanisms to show the movement of a pair of bonding electrons as a bond breaks or forms. The tail of the arrow marks where the electron pair starts and the head marks where it ends up. It matters because it makes the flow of electrons in a mechanism explicit and trackable. A full double-headed arrow denotes the movement of two electrons, in contrast to a single-headed (fishhook) arrow used for a single electron.

弯箭头,又称弯曲箭头,是反应机理中用以表示一对成键电子在断键或成键时移动方向的符号。箭尾标出电子对的起点,箭头标出其终点。它之所以重要,是因为它使机理中电子的流动变得明确且可追踪。完整的双钩箭头表示两个电子的移动,与表示单个电子移动的单钩(鱼钩)箭头形成对照。