Great Glass Elevator - Roof strength

But as the Great Elevator continued to streak upward further and further away from the earth, even Charlie began to feel a trifle nervous. 'Mr Wonka!' he yelled above the noise, 'what I don't understand is why we've got to come down at such a terrific speed.'

'My dear boy,' Mr Wonka answered, 'if we don't come down at a terrific speed, we'll never burst our way back in through the roof of the factory. It's not easy to punch a hole in a roof as strong as that.'

'But there's a hole in it already,' said Charlie. 'We made it when we came out.'

'Then we shall make another,' said Mr Wonka. 'Two holes are better than one. Any mouse will tell you that.'

***

Charlie and the Great Glass Elevator, Chapter 1