This was one of the first times I was invested enough in a book where the departure of a member of a group really shocked me.
There were a lot of shocks in this book for me, and with my frustration with Cassie as a hippie getting in the way of the animorphs defeating the evil aliens on my first read through versus my appreciation for Cassie as a primary reason the rest of them weren't dead after the first few missions and an example of the strength and relevance of empathy in every situation, I was pretty horrified spoiler
When? Cassie ripped out that hork-bajir's throat. And when she decided to leave the animorphs, that made perfect sense to me.
She had committed a brutal act that went so far beyond her personal boundaries that she couldn't be part of the group anymore.
That took me a while to come to terms with.
And then things get really terrifying when Cassie makes friends with a yeerk and makes a series of decisions that viscerally upset me to this day.
