Misplaced modifiers. The bane of writers and editors everywhere, from what I can tell.

“Even though he had practiced the trick for months, the rope failed at the last moment.”

Um . . . not quite. The rope hadn’t practiced (obviously, or it wouldn’t have failed, would it?). The fellow performing the rope trick had practiced, apparently to no avail. This is a misplaced modifier. More often than not in my experience fixing one of these requires rewording at least the latter part of the sentence. Here’s how I chose to fix this instance:

“Even though he had practiced the trick for months, he was unprepared for the rope to fail at the last moment.”