Knight move can hardly be called a sacrifice as it is quite
evident that Black cannot take the Knight on account of Qxh6+,
Kt-h7; Q-g7 mate. The only way to parry White's threat is (1)
..., Kt-g6. However, this helps only momentarily as White
continues (2) R-h3 threatening Q-g5, Rxh6+ and Qxh6 mate, a
threat against which Black has no defense. White can very nearly
force the mate by sacrificing his Queen on h6 instead of the
Rook. But after (3) Qxh6, Pxh6; (4) Rxh6+, K-g7; (5) R-h7+, K-f8;
(6) R-h8+ Black does not take the Rook as White would like him to
do to enable the mate R-g8, but he goes back to g7 with the King
and White could not do any better than draw by perpetual check on
h7 and h8.

+---------------------------------------+
8 | #R | | | #Q | | #R | #K | |
|---------------------------------------|
7 | | #B | | | | #P | #P | #P |
|---------------------------------------|
6 | #P | #Kt| #Kt| | #P | | | |
|---------------------------------------|
5 | | #P | #P | #P | ^P | | | |
|---------------------------------------|
4 | | | | ^P | | ^P | | |
|---------------------------------------|
3 | | | ^P | ^B | | ^Kt| | |
|---------------------------------------|
2 | ^P | ^P | | ^Kt| | | ^P | ^P |
|---------------------------------------|
1 | ^R | | | ^Q | | ^R | ^K | |
+---------------------------------------+