I can recount a lecture from a third party, which admittedly might be somewhat propaganda. When I was in junior high school, we had a fireman come by one day and give us “the talk” about fire safety, including some lecture about fire extinguishers. Here is what he told us about CO2 extinguishers:
It contains compressed CO2, which expands massively as it is discharged. Expanding gasses get very cold, and this will get cold enough to cause frostbite. (Here’s an experiment you can do at home: Open your mouth wide and blow gently into the palm of your hand. Note that it feels warm. Now purse your lips and blow gently into the palm of your hand. Note that it feels cool.)
Now, remember how if you go out on an ice-cold day and touch a frozen lamp post, your finger will stick to it? (Or similarly, if you touch a metal ice cube tray fresh out of the freezer.) Did you ever play that game of touching your tongue to a frozen lamp post?
Next, consider that all the expanding CO2 rushing out of that funnel will generate static electricity. Lots and lots and lots of static electricity. When enough builds up, you will get a sudden very strong jolt.
Now, have you connected the dots yet? If you aim the CO2 discharge by holding the funnel, it will get icy cold and the skin of your hand will freeze onto the funnel. Then you will get a huge static electricity jolt, and your arm will jerk away.
Leaving the skin from the palm of your hand on the funnel.
THEREFORE: Note that all CO2 extinguishers have, or ought to have, a wooden or plastic ring around the base of the funnel, which is where you should hold it to aim it. Here is the best pic I could find showing this. It is really really important for you to know and remember: HOLD THE FUNNEL BY THIS RING WHEN YOU DISCHARGE IT!!! Read the instructions on the side of the extinguisher in that picture – it even says so, although not quite as emphatically as it probably should.
ETA: So, fire extinguishers are the weapon of choice now for use by abusive boyfriends?