The Rise of Karzoug
When someone casts a spell or uses a spell like ability, there is disagreement about how much is visible. Verbal, somatic, and material components are obviously visible, but there are also additional audible and visible emanations.
Think of fantasy art spell casters, glowing eyes, floating runes, etc… accompany casting. As a house rule, spell modified by the Still Spell feat have no visual emanations and Silent Spells have no auditory emanations.