From Liveoak spell's text:
"This spell turns an oak tree into a protector or guardian. The spell can only be cast on a single tree at a time; while liveoak is in effect, you can't cast it again on another tree. Liveoak must be cast on a healthy, Huge oak. A triggering phrase of up to one word per caster level is placed on the targeted oak. The liveoak spell triggers the tree into animating as a treant."
Actually, I don't understand the purpose of that triggering phrase. What exactly is it supposed to trigger?
And what's the purpose of "one word per level"?
Other spells that make you decide a triggering word do not have such a feat (which is unnecessary, unless there's something I'm unable to see).