Thanks crisgal.
In fact, I came to this conclusion - although the moose / door interface description did pop into my head today - when I saw her on Countdown with the dreadful Whitely.
He was similarly devoid of anything approaching a sense of humour, so watching the two of them interact verbally was like hearing a nuclear scientist and a pygmie tribesman having a conversation - neither of them had a clue of the other was saying anything funny or not, but didn't dare admit it, so if one laughed (Whitely's laugh being a similarly mirth-free sound of a shed door being slammed repeatedly) the other would join in.
That meant that the originator of the comment - it was never important who said what - thought that what he or she had said must be funny, so they laughed along as well, and the two of them would sit and stand there braying at each other with the sort of facial expression one has when one sees an oncoming express train appraching the other person who has their back to it, and has no idea what's going on.
It used to give the feeling of a cat sliding down a blackboard, and I have avoided watching either of them since in any circumstances.
Gosh, I feel better now, I think I'll go and threaten one of the children!!!!!