What is missing in written language?
* in written language interaction works differently (e.g. turn-changes)
* hestitations / conversational grunts

* prosody: things like emphasis and so on
* pausing information: whether and if how long
* fundamental frequency
* speed

* semantics/intention that determines structure/stressing
* accentuation to focus on something (PETri nets vs. petri NETs); similarly to bold/italic font

* emotional condition  "You make me mad." (should be spoken like that)
* emotional coloring whispering/shouting/...
* dialectal variation
* loan words (pronunciation)

* word pronunciations (can be hard to recover; liaison); syllable stressing; 
* facial expressions and body language / gestures