他的背上有一个蛇形的红斑。

There was a red mark on his back in the shape of the letter S.

《新英汉大辞典》

在中美洲的一条街道集市，莎拉在她的肩上有一道小的蛇形的伤疤。

And at a street fair in Central America, we see that Sara has a small, pendant-shaped scar on her shoulder in the shape of a snake.

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“斯莱特林的记号。”他轻声说，光中闪耀着一个华丽的、蛇形的S。

"Slytherin's mark," he said quietly, as the light played upon an ornate, serpentine s.

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