23 FEBRUARY 2002, Page 67

Q. My parents have bought me a flat to live

in while I am at university, and this term I have invited in two fellow students to help with the mortgage. My problem is that while these two friends are perfect in every way, one of them has a slightly odd habit, which is that when cleaning her teeth she tends to walk round the whole flat in order to relieve the boredom of the two-minute cycle of her battery-operated toothbrush. Without appearing to pull rank, how can I put a stop to this habit and keep her in the bathroom during this period?

S. G., Edinburgh A. Buy up some unframed Victorian watercolours at a junk-yard and scatter these in the areas where your flatmate is likely to trespass. Next time she is going round the flat with her toothbrush, discreetly flick some personal detritus on to one of the watercolours, then cry out gaily, 'Oh look out! You've splattered this watercolour!' Her Pavlovian response will be to stay in the bathroom in future.