The way I see it, a mage can make a spellcraft check to recognize the just-cast spell in his vicinity an illusion (normal DC 15+level) and its name. He could automatically get an attempt to disbelieve it even from distance, and if he shouted a warning to his companions they would get a +2 or something bonus on their Will saves to disbelieve it when they interacted with it (like "it's only an illusion of a pool of acid, but do you dare to jump?).