I agree with lefteh, but there are different methods to it, that is something more of toucher, but as an ambush it is just done with a knife or box cutter and is quite sloppy. It is more common in the US for the second one, on the east coast it was something of a ritual to the Bloods on the east coast but on the west coast the Bloods were embarrassed by the east for doing such brutal acts to innocent people. I actually met a “famous” person from Glasgow with half of the smile, I should have mentioned that half is all they do if you’re not bound and are being ambushed. He appropriately addresses himself as Glasgow Ned, you can find his videos on YouTube, if you can understand the heavy Scottish accent you might find them quite funny.