Two girls were playing chess

Girl 1-I think we have played enough, I am getting bored..

Girl 2:You're right. Anyway, you are just left with a rook & I am with a knight..

Then a boy comes there..

Boy:Hey girls, Let's play some chess.

Both girls:No, You will beat us easily….

Boy:Ok, then. I will play against you two combined..

Both girls :Even then you will beat us..

Boy :Okay, I will play left handed….

Both girls :Sounds fair. Ok.

The girls, obviously, lose & the boy leaves.

Girl 1: This is so contemptible. He beat us even left-handed.

Girl 2 (after thinking for a bit ):OMG, he befooled us….

Girl1:How?

Girl 2: He must have been left-handed…