Being one of the trio of basic offensive area effect spells known to Wizardry, Effermhor's, like Pragi's Fiery Gaze and G'flott's Olfactory Nightmare damages all applicable targets in a room.

This particular spell creates a small cyclone of air, which then amplifies the screaming of the mandrake roots throughout the room, effectively dealing sonic damage. The spell is only moderately difficult, and failures of the spell result only in destruction of the jar of screaming mandrake roots, or on other occasions, the resulting removal of your clothing by the cyclone. Unlikely to be a pretty sight, but it will not hurt the caster.

 

The damage caused by the spell is quite respectable, like all the area spells. The normal average for most wizards would be between 1 and 1.5k hit points, or about three times their offensive bonus, with the possibility of more for powerful wizards. Like all of the area spells, the feedback messages you will receive on casting this indicate damage as a percentage term of the target's hps. The percentage ranges are estimated to be as follows:

Grating on nerves: 0-15%
Hurting ears considerably: 15-35%
Heads shuddering: 35-55%
Eardrums bursting: 55-75%
Blood oozing from ears and nostrils: 75-90%
Bones exploding: 90+%