What about Counterspells? Is it possible to counter (or identify) a spell without verbal or somatic components? (How does the caster know that I'm trying to cast a spell?)
A 43. Yes. A spell that lacks verbal and somatic components may still have material components or foci that need to be manipulated.
To cast a spell, you must be able to speak (if the spell has a verbal component), gesture (if it has a somatic component), and manipulate the material components or focus (if any). Additionally, you must concentrate to cast a spell.