Pull out all the words ending with "ing" in the passage below and put the words in alphabetical order. Don't include duplicates.
Here's the passage:
A beaver's long, dark-orange, visible incisors grow continuously throughout its life and are worn down through daily use. These teeth are self-sharpening and can cleave a willow the size of a person's finger in a single bite! If the incisors become too long, they can prevent the beaver's mouth from closing enough for its grinding molars to meet, which could lead to starvation.

Beavers regularly move between aquatic and terrestrial environments. Their small, dexterous front feet are well adapted to working on land. They walk on five digits, grasp sticks with their front paws and have well-developed digging claws. Their larger hind feet are webbed for swimming and void of fur, except on the dorsal surface.

The hind feet also have a preening toe, the second from the inside, with a unique double toenail. Beavers are meticulous groomers. They use the preening toe as a comb to prevent their fine, soft fur from matting to maintain its waterproofing and insulating properties. These flexible toes also remove burrs and parasites.
- closing
- digging
- grinding 
- insulating
- matting
- preening
- self-sharpening
- swimming
- waterproofing
- working