75 Once it was shown that the heroin was in the appellant's bedroom, the appellant was required to prove on the balance of probabilities that he had no knowledge that it was there. Putting to one side that the judge did not anywhere in her reasons explicitly expose for consideration the sole issue that she had to determine, upon the assumption - for the sake of argument - that she correctly directed herself sub silentio, there could only have been three reasons, alone or in combination, for rejecting the appellant's evidence of lack of knowledge. A fair reading of the judge's reasons suggests that she rejected the appellant's evidence that there had been a party with 'people coming and going' and 'using his room' (and thus that it was a realistic possibility that some unidentified person had left the drugs). As I have said, frail though it might have been, there does seem to have been some objective support for there having been a party. The judge may have rejected the appellant's version, first, because it was unsupported by any other witness (the judge observing that the appellant's was the only evidence, and she did not have 'anyone to say that it was a party and that people were sleeping all over the place'); secondly, because it did not accord with the probabilities; or, thirdly, because of the appellant's demeanour.