It bumps into the wall before it can do the leap it wants to, pushing up against it one more time to confirm - yes, there's now something behind it and it can't even climb it backwards. Smart thinking!

"It'll be gross and dead! Dex, drench it!"

Demyx - or Dexter - will see why as Tidus clenches his fist, pyreflies gathering around it - and then sparks. He's building up a spell, waiting for the water works to come down on the thing -

So that they can follow it up with a bolt. For extra wet-crispy uglyness.