In HoH:MC, the Illusion Mysteries include a Duration called While, which is described as follows:
While (Condition) (Duration):
The target must perform some activity, such as a musical performance or reading a book, or fulfill some common and temporary physical condition, such as sleeping or being drunk. As long as that condition lasts, the spell remains in effect. This is the same level as Concentration.
Does this mean that a spell with this Duration can only be cast on living beings? Or could you, I dunno, cast a spell on an inanimate object like a rock, and have it remain active for as long as the caster is singing or reading?