Here's why:
* They are multicellular: Leeches are made up of many cells, unlike bacteria or viruses.
* They are heterotrophic: They need to consume other organisms for energy, unlike plants which make their own food.
* They are eukaryotic: They have a nucleus and other membrane-bound organelles within their cells.
* They belong to the phylum Annelida: This means they are segmented worms, closely related to earthworms and other worms.
So, while they might be creepy and slimy, leeches are definitely animals!