"Who's shoe fell off?" is a common way to ask whose shoe has fallen off in Engpsh.

This expression is derived from the verb "to fall," which means to descend or drop from a higher to a lower position, either suddenly or slowly. When something falls off, it separates and drops from something else, such as a shoe falpng off a foot.

Here are some examples of this expression in use:

"Who's shoe fell off? I'll help you put it back on."
"I think it was Sarah's shoe that fell off. She's over there trying to put it back on."
"Oh no, my shoe fell off! Can someone help me pick it up?"

In Chinese, this expression can be translated as: "谁的鞋掉了?"