'Well,' said Holmes, 'when I examined Julia Stoner's bedroom,
I saw the bell-rope and the ventilator. I saw they were both
false. Then I noticed the bed was fixed to the floor.
'And I realised that something could pass through the ventilator.
It could travel down the bell-rope and land on the bed.
Immediately, I thought of a snake.
'Dr Roylott had other strange animals from India. It would be
easy for him to have a snake as well.
'So he kept it in his safe and fed it with milk. And every
night he put the snake through the ventilator. It went into his
stepdaughter's room and came down the rope. He knew that one
night it would bite the girl in the bed.'
'How did he make the snake come back to him?' I asked.
'Dr Roylott's signal to the snake was a whistle,' replied
Holmes. 'When the snake heard the whistle, it returned to its
master. Julia and Helen Stoner also heard this whistle.'
'On the night her sister died,' I said, 'Helen Stoner heard the
sound of metal clanging against metal.'
'That was the safe door clanging shut,' said Holmes.
'So when you heard the hissing noise in the room last night,' I
said, 'you knew it was the snake.'
'Yes. So, I hit it with my stick and it went back through the
ventilator. But the blows from my stick also made it angry. That's
why it bit Dr Roylott.'
'Dr Roylott wanted his stepdaughters' money,' I said. 'He
killed Julia Stoner and he tried to kill her sister, Helen, too. But
his plans went wrong. The snake finally killed its master.'
'Exactly,' said Holmes. 'And I don't feel very sorry for him.'