Look at the scene, it's a wound. There's no sound.
He just takes the plug out of the wound and plugs it into the tape recorder that Skull Face gives him.
So you're just making stuff up.
No, the real reason is that Kojima didn't know exactly what he wanted to do with the plot but probably figured early on it would have something to do with language. Chico is a left over from the initial concept of that plot.