– The picture displays the words “as thieves" two times, once on the top row and once on the bottom row. There is also a hand indicating the words on the bottom row. You have to pay attention to the difference in writing of the two set of words, as the one indicated by the hand is written in bold fonts, or in thick letters. So you have to place “thick" and words “as thieves."
– This expression’s meaning is similar to the meaning of “partners in crime" – people sharing a strong bond, or being very close friends.