Dangling or misplaced modifier
A dangling modifier occurs when a word, phrase, or clause is not placed closely enough to the word to which it relates:
She couldn't tell what kind of bird it was wearing her old glasses.
Problem and cure: While the sentence is grammatically acceptable, it suggests, erroneously, that the bird is wearing the glasses. The phrase "wearing her old glasses" needs to be closer to the subject, "She":
When she wore her old glasses, she couldn't tell what kind of bird it was.
A dangling or misplaced modifier throws a sentence into ambiguity, sometimes with unintended humorous results:
After roasting for three hours, I turned the oven off.
Of course, this sentence suggests that the speaker, the "I," has been "roasting for three hours," which, the reader can assume, can't be what was intended. Perhaps the writer meant to say something like the following:
After the turkey roasted for three hours, I turned the oven off.