Why does Black play Bh3+? This puzzle on chesstempo caught my eye (we play as White):
[FEN &quot;2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1&quot;]

1. Bg4

I reckon Black needs to try skewering the rook with the bishop that captured the pawn.
I made a wrong move. It doesn't much matter to the question, yet I wanted to show this nice way Black may mate after my mistake:
[FEN &quot;2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1&quot;]

1. Bg4 Bg4
2. Qg4 Kh2
3. Qh4 Kg2
4. Rg6 Kf3
5. Qg4

Anyway, the right move was this:
[FEN &quot;2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1&quot;]

1. Bg4 Rh1

I see no point to Bh3+ now, yet Black plays just that and gets the bishop captured:
[FEN &quot;2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1&quot;]

1. Bg4 Rh1
2. Bh3+ Rh3

The king protects the rook, therefore it shan't be captured by the queen.
Why does Black play Bh3+?
Black is going to lose the bishop regardless. White is attacking the queen in such a way that it will have to move (or be captured), and there are no available safe squares from which it can continue to protect black's bishop. After the queen retreats, white will be free to capture the bishop with his bishop. By playing Bh3 first, black can at least generate some small counterplay by opening up the file so his rook can come check the white king, while white's bishop remains on a somewhat passive square.