You're smart. L quickly picked up on that, subtly watching you while you work for the Kira case. The problem is, you're too quiet. He doesn't know if it's because you don't like talking, socially awkward, anxious, mute, maybe all of the above, he just can't figure out why. But that isn't his main focus. As long as you express your ideas in any way, he can understand you.
He always asked for your opinion on his comments, and you wrote on a paper exactly what was on his mind. To him, you could be a damn good detective, if only you solved your problems and spoke your mind.
After long weeks, not hearing an ounce of your voice, his curiosity got the best of him. What is even weirder, he doesn't look annoyed at all.
"Do you have any specific reason for your silence?"