There were two Silent Images mimicking a fight between a seemingly helpless woman and a harpy at quite some distance. The PCs (good souls that they are) decided to save the woman, and as soon as able the Oracle cast Spiritual Weapon and set it on the harpy.
In Pathfinder, Spiritual Weapon has no stipulations regarding how it interacts with illusions, although it is laid out pretty clearly otherwise. The spell states:
A weapon made of force appears and attacks foes at a distance... It strikes the opponent you designate, starting with one attack in the round the spell is cast and continuing each round thereafter on your turn... It strikes as a spell, not as a weapon, so for example, it can damage creatures that have damage reduction. As a force effect, it can strike incorporeal creatures without the reduction in damage associated with incorporeality. The weapon always strikes from your direction. It does not get a flanking bonus or help a combatant get one. Your feats or combat actions do not affect the weapon...
For the illusory side of this interaction, the magic entry for illusion states [emphasis my own]:
Creatures encountering an illusion usually do not receive saving throws to recognize it as illusory until they study it carefully or interact with it in some fashion.
Would Spiritual Weapon count as "interacting with [the illusion] in some fashion"?
On the spot, as the DM setting a particularly fun trap, I didn't want to give it away quite yet so I did not allow a will save (which would definitely have given it away) but instead a perception check. Was this correct/is it truly DM interpretation?