lateral thinking – A strange chess variant

Alice and Bob are playing some weird variant of chess. They somehow arrived at the following position:

Alice, with the white pieces, plays: King f4

Bob, playing black responds: Queen g4

Alice: Knight from f5 to h6

So what are they actually playing? More importantly, what should Bob do on his next move?

Hint 1:

Alice and Bob would prefer to shift all the pieces on the board slightly but unfortunately that is not allowed in standard chess notation.