There was a note on the

kitchen table when I returned home yesterday. "Please ring...."
The Senior Cat had taken the message while I was out. He had not taken any other message. The person who wanted me to return the call needed to speak to me as well. 
I went and reported my return to the Senior Cat and said I would return the call. 
The number was engaged. I tried an alternate number. Nobody was answering that. I went on trying throughout the day. It was fairly clear by then that the phone had been taken off the hook. I had no idea whether it was deliberate or accidental. 
It was much too warm to pedal over to the home in question. It would have taken about twenty-five minutes to get there. If something was seriously wrong then I thought I would hear soon enough.
At five-thirty in the afternoon the phone rang. Yes their phone had been off the hook and no it was not urgent although she did need some advice. I gave her the name of the person she needed to see but it was clear that there was something else wrong. Why had the phone been off the hook? 
There have been occasions when the Senior Cat has accidentally failed to put the receiver back properly after answering or making a call. The result has been no incoming calls - until I have checked and rectified the matter. He hates it when he does something like that. 
For my caller however it was a different matter. Her sister had deliberately taken the phone off the hook at the extension in her bedroom. She "did not want to be disturbed". 
Her sister is a not well controlled diabetic who believes she can handle her diabetes and who refuses to listen to medical advice. The result is that, much more frequently than she should, she has had episodes of low blood sugar. When these occur she becomes irritable, moody and even violent. It is impossible to reason with her. She refuses to take in any food or drink to alleviate the symptoms. On two occasions in the last three months she has been taken to hospital in a semi-conscious state. 
Taking the phone off the hook yesterday was all part of this. Even if we point out to her yet again that this is dangerous it will make no difference. She will merely point out that her sister dealt with the situation, that there was "nothing to worry about" and that "these things happen occasionally".
I think there is something to worry about because her behaviour is causing problems for other people as well. The last time it happened the Whirlwind, who also knows them both, said, "But she's not being fair - like people who smoke or people who get drunk and end up hurting someone else."
How do you explain this sort of behaviour to a child with a very strong ideas about what is right and what is wrong?