I think the point is that they don't have "cell walls", animal cells have "cell membranes". I'm not sure it's that relevant here since cell size seems more impo

I think the point is that they don't have "cell walls", animal cells have "cell membranes". I'm not sure it's that relevant here since cell size seems more important to tolerating the spikes, but hopefully this helps explain the comment. I'd really only considered plants as having "cell walls" prior to this.