Flaw in the Flea Flan (Book 21)

Cassie nearly dies and then talks Marco down from being stuck as a giant flea. David the Lion behaves badly beneath a fancy table. Something something force field enforced holograms.  

How sanitary are Yeerk pools if they're always exposed to the open air? We’ve already seen Rachel the bat fall into one in a cave and now there's one beneath a gaping hole in a roof! Is saying "bite me" to someone antagonistic or flirtatious? How is anyone in the fandom so critical of Cassie when she has amazing moments like saving Marco from his flea morph? What the hell is going on in this book with holograms and force fields?