Illusion

Illusion spells deceive the senses or minds of others. They cause people to see things that are not there, not see things that are there, hear phantom noises, or remember things that never happened. Illusions come in five types: figments, glamers, patterns, phantasms, and shadows.

Saving throws and illusions (disbelief)
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. For example, if a party encounters a section of illusory floor, the character in the lead would receive a saving throw if she stopped and studied the floor or if she probed the floor.

A successful saving throw against an illusion reveals it to be false, but a figment or phantasm remains as a translucent outline. For example, a character making a successful saving throw against a figment of an illusory section of floor knows the "floor" isn't safe to walk on and can see what lies below (light permitting), but he or she can still note where the figment lies.

A failed saving throw indicates that a character fails to notice something is amiss. A character faced with proof that an illusion isn't real needs no saving throw. A character who falls through a section of illusory floor into a pit knows something is amiss, as does one who spends a few rounds poking at the same illusion. If any viewer successfully disbelieves an illusion and communicates this fact to others, each such viewer gains a saving throw with a +4 bonus.