Which link in the chain of infection does the situation portrays: daria doesn't cover her open sore and later watches tv with her roommate on her roommate's bed. they share a bowl of popcorn.

This is definitely ‘mode of transmission’. Ingestion

To view their body language, it's a huge part of spoken language as it can define what type of speech it is. For example if they have their arms close in they may not want to speak to you or if they are doing lots of hand gestures they are explaining something.