She had spotted the culprit with her cornflower blue bone china mug with tulip design around the rim. There was no friendly acknowledgement or joke. No. A glare, a look of horror. I moved away for fear of having my own mug whipped out of my hands.
I glanced over just in time to find the teacher in question returning from the direction of the sink, cornflower blue mug in hand, looking smugly into her instant soup.
The thief watched in disbelief. I vowed never to go without a mug - or, indeed, to be one.
2. Reading matter. I carry Bridget Jones' Diary for a few minutes escapism at lunchtime. The danger with English teachers and magazines, or "literary texts" as the national curriculum calls them, is the tendency to pick up ideas for lessons or essay titles. So the text must be unrelated to your subject.
I looked at the reading matter on the staffroom coffee table today and found: a leaflet advertising special rate personal loans for teachers (is that how bad the pay is?) a magazine which I can only guess had something to do with the decorative state of schools, since it was adored with a photo of Carol Vorderman brandishing an electric drill.
3. Chocolate. The only source in my school (apart from the canteen's dubious chocolate cake) is in the sixth-form block. Not a problem, you might think: just stroll over to the machine, greet the students at the pool table, coolly acknowledge the music, which is invariably at full volume and get the Mars Bar you need.
But when you're a PGCE intern, there's always the danger that you will be mistaken for a sixth-former just minutes before you attempt to appear as teacher in the last lesson of the day. Best to come prepared, I say.
4. Biros. Simple, yet important. I have lost at least five pens in as many weeks - not from lending them to forgetful pupils, but from leaving them on a staffroom table for more than a minute.
5. Invisible rhino hide. On my tutor's advice, I will wear a rhino hide for my entire teaching career, not least my PGCE year. This should prevent me sobbing to friends about the Year 9 girl who laughed at my dress sense.
6. Diary. For noting in-service training courses, parents' evenings, school plays and the like, and as a reminder of your other life. You can always colour-code school and social events differently, although one colour may be used rather more than the other.
Katherine Lee is studying for a PGCE at Oxford University