The rules on somatic components are clear:
A somatic component is a measured and precise movement of the hand. You must have at least one hand free to provide a somatic component.
A naga generally casts spells like a cleric or sorcerer, which should mean that they follow the same restrictions as those classes. Does this mean that a naga and creatures like it with actual spellcasting abilities cannot cast spells because they don't have hands?
Best Answer
The designers don't think this is an issue
The Monster Manual for D&D 3.5 in its glossary entry on Spells included this:
…Yet similar text is absent from the Bestiary for Pathfinder. So this became kind of a big deal, discussed at length in a 2010 Paizo messageboard thread. In that thread, creative director James Jacobs eventually says in this post that
…And the thread is shortly thereafter locked, the matter considered resolved by the Pathfinder staff.