Last week I was DMing the Red Hand of Doom adventure. Outside of the Varaath keep the rogue, sorcerer, and bard were all going invisible in various ways. The half orc barbarian picked up a hand full of sand, threw it above him, and screamed "I'm invisible too!" Which caused the monsters inside the keep to come running out and attack them. Way to go, Hector the Well Endowed. Way. To. Go.