He couldn't have, he made a phone call to Bamber after being out cold for four hours and nursing three burn marks to his back and never mentioned anything to JB.
We dont know yet how long the burns took to form HB,but if they occurred before Nevill phoned JB at 3.10 we have roughly four hours or so to play with,about 11.00 until 3.00.Boyce will have carried out experiments to determine this,although,as Bubo has pointed out,Boyce is working on the assumption that Nevill was already dead while he lying against the Aga,and besides,how do you get a living person to lie against a hot Aga and be experimented on?
Anyway,we will just have to wait and see what Boyce has come up with.
As for the marks,they seemed to be deep third degree burns with the skin destroyed so Nevill would have felt no pain from them and been oblivious to their existence,besides,his attention would have focussed on his thumping sore head.
As for making the call to JB,we dont know the severity of the brain trauma caused by the blow to the head.Amnesia may not have been present,all he may have remembered was Sheila smashing the rifle over his head,hence'Sheila's gone crazy and she's got the gun,youv'e got to help'. Thats obviously all he would have known at that stage and therefore slammed down the phone to rush upstairs and see just what Sheila had done.