Like, let's say there is an illusion of... a potted plant in the middle of the room. The PCs look at it and see a potted plant. The srd says they get a will save if they "interact" with the illusion. So one goes up and touch the plant. What happens if they fail their will save? They touch the plant and it feels real? What if they fail, then they stick their arm right through it? Now what do the other PCs see? Can one still bomb a will save and so touch the plant even after seeing someone else walk through it? I can't find anything in the srd, and I don't recall Wizard's giving any hints. How do you guys play it?