Splash Damage does not trigger "Tooth"
I've always wondered why Malphite and Nocturne are so bad at clearing camps designed for AOE junglers, and I've finally noticed - effects such as Tiamat, Umbra Blades, Brutal Strikes, Fishbones, and Call of the Freljord are not applying the Tooth bleed/healing to monsters.
This seems weird, because Tooth says it applies to "your damage", the same wording that is used by Gunblade - which does apply to splash damage.
Maybe it's not a bug, since it seems consistent - but it doesn't seem right.
UPDATE: As of 8.19, Nunu has been changed to trigger Tooth. Lucky him.