For some reason I'm flashing back to reading the animorphs (like 20 years ago) and remembering Jake (I think) commenting when he turns into either a hippo or a rhinoceros on the irony of such a large animal essentially tiptoeing everywhere. In retrospect you really could tell how passionate K.A. Applegate was about evolutionary biology. What a colossal nerd. Good times. Excellent book series.
You should reread the series if you only read them as a kid. They get surprisingly dark, I missed a ton when I first read them as a pre-teen. Still enjoyable and short enough to burn through quickly.
I remember grasping a remarkable amount as a child #justshittychildhoodthings but I could use a re-read and I'll need something at about that reading level in Spanish at some point.