本日の英語フレーズ　 Today’s English Phrase

Meaning: to have a secret advantage that is suddenly revealed to change the game. A hidden resource.

Example:
1. He did not just leave his house. He had a card up his sleeve that he did not even reveal to his family, which was his new flat in a posh locality.
2. The competition should always be checked for cards up their sleeves when you can.