If he's being honest, the correct play would be scissors.

But it's foolish to assume he's being honest, so layer 1 of dishonesty says he's trying to get them to throw scissors so he can play rock. Therefore the correct play would be paper.

But it might be a 2 layer lie, where he intends them to see the first layer and play paper to defeat that expected rock but instead play scissors to defeat their paper. Rock defeats scissors.

You can reason your way to any play in rock paper scissors based on how much deception you think your opponent is using. Add another layer and you shift the moves by one.