To try your best to think; make a great mental effort; especially: to try to remember something you have known.
Напряженное думать; особенно в ситуации когда нужно запомнить то что обязательно надо знать.
Bob racked his brain trying to remember where he left the book.
John racked his brain during the test trying to solve the problem.
She was racking her brains for something to say.
Она напрягала мозги, чтобы что-нибудь сказать.
Susan racked her brain trying to guess whom the valentine came from.