Because she does not understand the American rules of chess
The root word is movable because it can stand on it's on as a word, while "im" can not.
If I'm understanding you correctly (sorry, I'm new at this) It sounds like you are describing an accident that either didn't actually happen, or was minor compared to what could have happened. I would call this a "near miss" or "close call"
Explanation:
For example: I had a near miss today when a dog ran out in front of me.
Or: He had a close call when his foot almost slipped over the edge of the cliff.
D because it says that he was mad AS hell. A simile uses like or as.