Facilitating in the dark

I'm a huge fan of distributed, & open ways of working, but it is not without its challenges. Monitoring the vibe when facilitating a workshop via video conferencing is particularly tricky.
 
In person, we can easily read people's body language.  Those who are not speaking are still contributing their time, their attention and their energy. We can easily see if people have become bored, or are distracted.  Online it's hard to sense if lurkers are learning, listening, thinking, multi-tasking, or just completely tuned out.
 
If people on the call are not participating that's ultimately their choice, but as a facilitator I feel I have a duty of care to give those people some safe way to indicate they're bored, or disengaged.
 
Common practice suggests we should ask participants to have their video on. But it's not always possible due to bandwidth limitations or poor connections. Plus there's a growing understanding that video calls are exhausting, so it's not fair to demand that everyone be on camera all the time.

I'm keen to hear what others think about this. 

What are your strategies for facilitating in the dark? 

Tell me via twitter

Image Credit: Red Hat Illustration Team