Siobhan said:
Like in the Omen when the nanny killed Damiens mum, injecting air into her arm.
Sorry people, but the pedant in me really can't resist

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This is a Hollywood variation of an urban legend! What is called "gas embolism" (i.e. a bubble of air being introduced directly into the blood stream) is almost always harmless. It often happens after surgery, and small air bubbles are quite commonly introduced by injection or intravenous drips. Usually this causes no symptoms whatsoever, and the air is just absorbed into the body over a few hours or days. Sometimes a large bubble lodges in tissues, at which point it can become uncomfortable - but it is still harmless and usually absorbed without any problem. Extremely rarely, a very large bubble can lodge in the heart blocking the blood flow. This can cause a heart attack, which could be fatal. However, even if you were to be injected with a completely empty syringe, although I wouldn't recommend it, you would be very unlucky to die. So, I am afraid, as a means of either murder or suicide the injection of air really doesn't cut it!
Insulin is a different matter, however. A large enough dose will quite quickly put anyone - diabetic or not - into a coma, and if that isn't treated they most definitely will die. However, this really isn't dangerous knowledge. If you are looking for ways to kill yourself or anyone else, then most prescription medicines will do the job, as will a bottle of paracetamol or even weed-killer! I am sure that everyone knows this, and it is important that they do because you need to be careful when handling medicines or toxic chemicals!