Do you feel safe?
Recently I was doing some training and a person told me beforehand that they don't like to contribute in a group. I asked them if I could involve them by asking one question. I told them when I would ask them the question and told them what the answer would be. They agreed.
I kept an eye on them to check they were ok, then at the right moment, asked them the question. They gave me a big smile and answered. Then they continued to volunteer answers after as they felt safe enough to take the risk in that group.