The first move of the Bird's Opening.

Black has a number of replies. c5 aims to counter White's pressure on the central dark squares with moves like Nc6, d6, and g6 and Bg7.

Not a good move as I missed White's reply.

A sharp response threatening g5 followed by Bxh8

This is a risky and complicated response that offers a pawn for play and quick development if White goes for it. Bg7 or Rg8 are safer moves here:- 4...Bg7 5 g5 Nh5 protects the bishop.

Sensible to block the d8 h4 diagonal irrespective of the pawn win on the grounds that Black has the discovered threat of Qh4 mate in some lines if the knight moves from f6. I would be surprised of this position was known to theory. Both players are thinking on their feet and trying to stay upright!

Attacking the bishop and thus encouraging white to take the pawn.

This move gains a tempo for the development of Black's light square bishop. If f7+ then Kxf7 and Bxh8 fails to Qh4 mate.

Black has now saved the h8 rook and can look forward to playing Bg7, 0-0, Nc6 and Bf5. White has the extra pawn but has weak squares on his kingside and less central influence.

Gives the king a flight square against so the threat of Qh4 mate is eliminated.