Hopping on the bus, my keys fell out of my pocket.
That’s a dangling participle.
The participle, “Hopping on the bus,” appears before the main clause, which is often the case with participles. However, in this case, the participle appears to “dangle” because it does not refer to “my keys fell out of my pocket. This is because ” on the bus” is not immediately followed by “I,” but instead by “my keys.”
You may say that no one would read this sentence and think that my keys were hopping on the bus (at least no English-speaking reader would think so), but with language, clarity is important. Even an English speaker might have to read the second twice in order to perceive its meaning.
Dangling participles can be avoided if you carefully read over what you have written, looking for ways in which your meaning might be misinterpreted. Your reader is like an invited guests: you want to make them feel as comfortable as possible, so that they will feel at home with your thoughts.