Here's why:

* Animals are multicellular: Leeches are made up of many cells.

* Animals are heterotrophic: Leeches cannot produce their own food and must consume other organisms (blood in the case of leeches).

* Animals are eukaryotic: Their cells have a nucleus and other membrane-bound organelles.

* Animals move: Leeches can move and are not stationary like plants.

Leeches are further classified within the Animal Kingdom as follows:

* Phylum: Annelida (segmented worms)

* Class: Hirudinea (leeches)

Let me know if you'd like to know more about the classification of leeches!