I believe the biting of the tongue is Chibi-Miku trying to pronounce the "th" sound, which doesn't really occur in any modern language other than English, and is made by vibrating the tip of the tongue and the upper front teeth together with a hum-like vocalization. To get one's tongue into the proper position, gently biting the tip of the tongue serves nicely, but Chibi-Miku obviously bit hard rather than gently.
