ending

his wife has the habit of wearing a bracelet on her left hand, there was a scene about it before, that states so
and when he was looking at them, he noticed it was on her 'right hand', thus knowing that they were behind him

but if that was the case, there would be a loophole: he would have seen himself in the mirror as well, and in fact, blocking their image

but despite alittle loopholes, this is a fantastic movie