e6.
The explanation is in white, so Irontiger can easily avoid to read it:
Calculating captures: after fxe6 Bxe6 dxc5 Bxc5 have we advantage in development. Not good for white.
the DSB is developed, the pawn on f5 threatened to recapture, hence will white play a non developing move like fxe6 or g4. Maybe is Qf3 an alternative, but then can't play white the knight not anymore to f3 (looking at the hole of e5).
fxe6 helps black to develop, g4 gives black a clear target if white should castle kingside.
Therefor will I expect Nf3 Nc6 Bg5.
My face also likes c4.