I have 22 int and sometimes when I stun creatures it doesn't last at all. It's not that they're unstunnable or saved the stun either.

(171 H 30 M): Stun cast on greater aboleth.
(171 H 20 M): k gr
Please wait 1 more second.
(171 H 20 M): l gr
You see a greater aboleth.
A very huge amphibious creature with flailing dangerous tentacles.
He is in excellent condition.
He looks very angry at you.
He is attacking you.
He might be tough to kill.
k gr
(171 H 20 M): You FUMBLED your weapon.
use stormblade
You punched the greater aboleth for 0 damage.
k gr
(171 H 20 M): You wield a stormblade.
You feel a thunder-like rumble in your hand.
k gr
(171 H 20 M): k gr
Please wait 3 more seconds.
Please wait 3 more seconds.
(171 H 20 M): Please wait 3 more seconds.
(171 H 20 M): k gr
k gr
Please wait 2 more seconds.
k gr
(171 H 20 M): Please wait 2 more seconds.
(171 H 20 M): Please wait 2 more seconds.
k gr
(171 H 20 M): k gr
Please wait 2 more seconds.
(171 H 20 M): k gr
The greater aboleth casts a waterbolt spell on you for 19 damage.
Please wait 1 more second.
(152 H 20 M): k gr
Please wait 1 more second.
(152 H 20 M): k gr
Please wait 1 more second.
(152 H 20 M): k gr
Please wait 1 more second.
(152 H 20 M): k gr
Please wait 1 more second.
(152 H 20 M): k gr
You slashed the greater aboleth for 20 damage.
(152 H 20 M): k gr
Please wait 3 more seconds.
(152 H 20 M): Please wait 3 more seconds.
(152 H 20 M): The greater aboleth tentacle-slapped you for 47 damage.

Aboleths are Mage/Lich stun. Any monster with this flag will now output a message.