Let us watch the process.
He had found a half-fledged mavis lying dead in the grass.

Remember also how the larks had sung after rain.
Tommy lost sight and sound of Corp and the boy.

What he seemed to see was a baby lark that had got out of its nest sideways, a fall of half a foot only, but a dreadful drop for a baby.

"You can get back this way," its mother said, and showed it the way, which was quite easy, but when the baby tried to leap, it fell on its back.

Then the mother marked out lines on the ground, from one to the other of which it was to practise hopping, and soon it could hop beautifully so long as its mother was there to say every moment, "How beautifully you hop!" "Now teach me to hop up," the little lark said, meaning that it wanted to fly; and the mother tried to do that also, but in vain; she could soar up, up, up bravely, but could not explain how she did it.