He did not know this at the time because, for some reason or other, he forgot to wind it up when he went to bed (an unusual occurrence with him), and hung it up over his pillow without ever looking at the thing.
Il ne s’en aperçut pas sur le moment, car, pour une raison ou pour une autre, il oublia de la remonter avant de se coucher (ce qui ne lui ressemble pas), et l’accrocha au-dessus de son oreiller sans meme la regarder.