Two loose bishops on the same rank, like two rooks on the same diagonal, often are prey for a skewer, as White has shown here by playing his rook to d6. What can Black do about it? Again, the first line of defense against a skewer often is an interposition. Black can get a piece between his bishops and White’s rook with Rc6. The critical point is that the interposing piece must have protection; else White just renews the skewer with RxR and gains material to boot. Here Black’s knight protects his rook on c6, so interposing the rook defuses the threat.
There is a fancier defensive idea worth seeing that works as well. Black can play 1. …Bf2, launching a counterthreat; now if White plays RxB, Black has BxN and has just traded minor pieces. The consequences of Bf2 are more complicated than this, though, as White can reply to it with 2. Nd3—removing the knight from danger and using it to attack the bishop that was menacing it. Indeed, now both Black bishops are under attack by different White pieces. Yet Black has effective replies to this as well: 2. …RxBc2; 3. KxR, BxNd3+ (the point of RxB was to clear the diagonal for this capture); 4. RxBd3, NxRd3; 5. KxNd3—and now the only pieces left on the board are a White knight and a Black bishop! A little more simply, at the third move White can skip KxR and play RxBa6, which gets even but ends the bloodletting as Black now moves his rook to e2 where it is safe and can guard the bishop at f2.
The lasting point of this messy exercise is to see the value—and also the difficulty—of replying to a threat by making a new threat of your own elsewhere. This can be a surprising and effective option for breaking out of tactical trouble, but it often isn't for the faint of heart; it can give rise to lots of complications, as both threats may play out and interact with each other.