It's literally not that deep, Skulduggery, it's that you're wearing the wrong head! With no explanation! (And he's told her before that it wasn't even his original skull, but she'll only think upon that later.)

The swing of his fist connects with the side of her face, and that's it. That's part of the prove it test that she so hastily scraped together, and he's failed. Because Ava has no reason to believe the real Skulduggery wouldn't hit her, if provoked, but in the moment it's enough flimsy evidence. None of this seems right.

"You got his face wrong!" She barges through the perceived imposter, grabbing his much taller frame from behind, and throws her weight to crash them both through the floor and down to the next.