In Borderlands there is an in-game trophy system. The very first trophy is titled 12 Days of Pandora and involves killing lots of things in many different specific ways. One of these ways is apparently face melting, as I'm currently listed to have 1\2 of my "Faces Melted" entry. I have no idea how I got the one I already have, and would very much like to re-create the event, as completing this entry will finish this trophy for me.
How do I melt faces?