I too agree with NN's scenario. Maybe Sheila had locked herself in the downstairs toilet or something? Whatever,but Nevill must not have considered Sheila an "immediate" threat at the moment he phoned JB.Whilst on the phone,she may have rushed upstairs,which made Nevill panic and put the phone down,only it didn't get put down properly.I don't believe he was injured in any way when he made the call.If that was the case,I don't believe he would have asked JB to come over,wouldn't have put him in danger.He clearly didn't expect Sheila to use fire the rifle.