A twig that he thought a long way off, would the next instant hit him on the nose or rake along his ribs.

There were inequalities of surface.

Sometimes he overstepped and stubbed his nose.

Quite as often he understepped and stubbed his feet.

Then there were the pebbles and stones that turned under him when he trod upon them; and from them he came to know that the things not alive were not all in the same state of stable equilibrium as was his cave--also, that small things not alive were more liable than large things to fall down or turn over.