Coloured ballpoint pen is a good medium for depicting fur on animals, particularly since animals tend to be coloured in some shade of brown which is easier to blend when your range of available pen-colours is limited. Any pair of opposite colours will give you brown, so you can slather all sorts of colour everywhere to add great nuance to the picture.

Animals are also a good subject matter because the distinctive appearance of each species means you can take great liberties with the animals' expressions and gestures without obscuring the nature of the animal. This is good for creating "cute" animals by varying aspects of their appearance.

On the other hand, pastel animals provide a very "painterly" feel and have greater colour accuracy which is good for a more contemplative feel.