The following text is for questions 48 to 51.

An earthworm uses its pointed head end to dig a hole in the soil. It searches for loose soil and forces the soil apart. Slowly, the worm draws the rest of its body until it disappears into the hole. The earthworm has many narrow rings which enable it to change shape.

    The earthworm will eat the soil if it is too hard to be pushed aside. It opens up channels through which air can enter by burrowing into the soil. Because of this, the soil will be oxygenated. The roots of plants planted in that soil can breathe. In this way earthworms act as gardeners and cultivators of the soil. 

" ... by burrowing into the soil." (Paragraph 2)

The underlined word means ....