If you deal some damage believed to be over 33,037 via a +6 Kyogre with full HP using Water Spout on a low level Geodude (or Sandshrew I have heard, I used Geodude for my video), then it will faint without its HP bar draining. This does not occur in FireRed or Emerald.
One of my Youtube viewers Huskies Plays asked me a question taking this further. What if Kyogre had max Special Attack and 65535 HP out of a normal full HP value before using Water Spout?
Something interesting happens and this glitch occurs in FireRed and Emerald the same as well! The HP bar of Geodude drained, but it seems that no damage was dealt. Opening the Pokémon or items menu and closing it refilled the HP bar. I could use Water Spout again a few times before it finally fainted. Sometimes the HP bar stayed fully green and other times it drained.
Unfortunately when I caught it with 5 party Pokémon after its HP bar drained/didn't change it had full HP.
Note that to do this glitch you have to disable battle animations to avoid Water Spouts' Pomeg sprite glitch (but that is arguably more cool than this glitch I think).
Edit: Forget the 'finally fainted' thing. That may be a false memory. On further analysis, it seems the game does negative damage. Lower Geodude's HP with another Pokémon and repeat the glitch. This will make it so that using Water Spout heals Geodude.
Edit 2: Hey, I wonder what would happen if the opponent used Mirror Coat after you healed them with Water Spout? Perhaps you could do this:
1) Have a Smeargle with Skill Swap. Skill Swap with Kecleon to give it Color Change.
2) Have Smeargle used Endure on an Earthquake to make it the Ground type
3) Lower Smeargle's Special Defense with Metal Sound.
4) Set up and finally use Water Spout, and then have Smeargle Mirror Coat it.