What are the steps that should be taken if someone you're hiking with starts to sink uncontrollably into say a marsh? What are some good techniques and points that should be used to get them out safely and quickly? I'm not talking about times when their feet might get a bit wet, I mean when someone suddenly starts going down, it's clearly a real danger and you need to act quickly. Is there a type of rope that's good for this, good knots or anything like that? Things to practice?
Equally, what's best to do if this happens to you and you're alone?