If Garrot was expecting some magnificent fanfare, some kind of world-shattering entrance, some sort of shock-and-awe arrival on Twelve's part when he comes to knock on her door, he'll be massively disappointed. Because her door is closed, none of the other monsters are shuffling around to see what's about to happen, and he gets a response to his knock.

In the form of his same, identical knock coming back from the other side. Same weight, same height, same rhythm. How odd!