Metal Utensil to Save Your Glass

I often have to pour hot or boiling liquids into glass jars, such as this bacon grease). Unless the glass is tempered, it will shatter. Someone told me that if you stick a metal utensil in the jar, somehow by magic it prevents the glass from breaking!

I have tried it with every kind of boiling thing possible, and I dare say it works. I'm not sure why it works, but all I know is that the fork/knife/etc gets very hot to the touch, so maybe it sucks up some of the heat.