The situation looks unfortunate for Black, does it not? He was caught with his queen and rook on the same diagonal, and now White has played his bishop to d6, skewering them with protection from the pawn on c5 and apparently ready to win the exchange. There is no room for Black to interpose anything, and he has no checks. What else could be left? Again, a mate threat. Always remember to consider what pieces you have trained on squares next to the enemy king. Here Black has a bishop aimed at g2. If he can tear his queen out of the skewer and attack g2 with it at the same time, White will have to waste a move avoiding the threat of Qxg2#. So Black plays Qg5 and then relocates his rook on the next move, ending the threat of the skewer.