How to prove sand is not a fluid even if it takes the shape of a container

Solids can be any size or shape. Sand is a solid that has the ability to be poured like a liquid and take the shape of its container. It is still a solid, as each individual grain of sand has a shape of its own and keeps that shape.

Explanation:

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.