Insidious Rhythm

Song and Silence: A Guidebook to Bards and Rogues (SaS)Updated Supplementals (3.0)

Insidious Rhythm is a D&D 3.5 spell (Enchantment (Compulsion)) from SaS. On class lists for Bard (Level 6), Bard Variant (Level 6), Divine Bard (Level 6), and others. Range or area: Medium (100 ft. + 10 ft./level); Saving throw: Will negates; Duration: 1 hour/level; Casting time: 3 full rounds.

School
Enchantment (Compulsion)
Casting Time
3 full rounds
Components
V, S, F
Range
Medium (100 ft. + 10 ft./level)
Target
One creature
Duration
1 hour/level
Saving Throw
Will negates
Spell Resistance
Yes

The caster plays a catchy, silly, little tune that sticks in the mind of any subject who fails a Will save.
The endlessly recycling melody makes it very difficult for the subject to cast spells, disarm traps, or perform any other action that requires mental focus.
Thus, the subject incurs a -4 circumstance penalty on all skill checks based on Intelligence and must make a Concentration check (DC = insidious rhythms save DC + level of the spell being attempted) for each spellcasting attempt.
Focus: The caster’s instrument.