KaaTun is a rare Runeword created by combining a Kaa Rune of Ritual and a Tun Rune of Invocation.
How to Create KaaTun
You can create KaaTun by adding the rare Kaa Rune of Ritual and the magic Tun Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Kaa - Lose 1% of your Maximum Life. (2)
Tun - Evoke the Rogue's Stun Grenades, Stunning and dealing damage to enemies. (100)
Overflow
KaaTun can not overflow because the amount of Offering you receive from the Kaa Rune exactly fills the required Offering of the Tun Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.