Working day Wednesday this week

So I was working on a clutch system under the bonnet when our two 17 year old apprentices came to me and asked about some type of exhaust sensor but explained it sounding more like a GPF. At first I thought the young lad said GPS! but he said no GPF. He said it was some type of sensor in the exhaust system but I said to him I don't recognise the abbreviation? As we were talking the boss in the next bay doing an mot said to us, quite abrutly and I kid you not, Do Not Talk to one another unless you are in your own time! Really?