Funny how something like a Bishop move makes one realise this

The idea being to allow f4 to be taken

? But this doesn't work, as White can play RxN (if then fxe4 then Rf1 wins the Queen, and if dxe4 then White simply plays c3-c4, which is a strong threat to g7, and the Bishop on d7 is hanging)

RxN was missed however

? So Black gives White a second chance, this time easier to spot, as the f-pawn is already pinned and the Queen is hanging on d6, so there's no dxe4

This allows the fun to begin, Black can gain a strong central position with these pawns, all with tempo

Breaks the pin... but Black is not in time to take on e3, as his own King is being aimed at

Intercepts, also removing the use of some squares for White

That h-file looks promising...

Perhaps hoping for bxc4, but