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Q: When I eat toast in the morning (particularly wholemeal with crunchy
bits), I notice that the green glowing symbols on the clock/timer of my
microwave bounce up and down in a sort of rippling manner. However, the
green symbols on the gas cooker clock (a slightly different hue) can only
be persuaded to take exercise with the most strenuous mandibular effort.
The red LEDs on my old calculator also appear lethargic. It I bounce up
and down, the whole microwave, including the display, seems to bounce up
and down in anti-phase. What is going on?

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A: The microwave oven symbols are obviously flickering at a rate not
discernible unless the eyes make sudden movements. If the questioner finds
his entire microwave oven bounces up and down when he does (what-ever the
phase relationship) then maybe he should consult a builder about his kitchen
floor! Bruce Edwards Norwich

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A: Eating things like toast causes movements of the eyes (perhaps by
shock waves induced by the crunching) which can move an image to a different
point on the retina. Most multidigit electronic displays illuminate each
digit in turn, relying on the persistence of vision for the appearance of
a continuous display. However, rapid head movement means that during successive
illuminations, the image of any digit may be displaced, giving a rippling
movement. If one finds this disturbing, porridge is a good breakfast alternative!
Roger Blackwell Leeds

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A: I get shimmering timers too, but not by crunching toast. I sing a
deep B flat – just more than two octaves below middle C. The resonance seems
to cause the cranium to vibrate and hence the field of vision. It is more
noticeable on electronic displays because of their inherent ‘shimmer’. Immodesty
compels me to add that not many people can sing this low, so not everyone
will be able to confirm this, unless, of course, your wholemeal bread is
pitched at B flat. Presumably different craniums resonate at different frequencies,
so other bass singers may report different critical notes. Peter Morgan
Beckenham, Kent

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A: I sometimes gaze at my television from across the room, crunching
peanuts. With every crunch, the picture height dances rapidly, appearing
first as short and then as long. Further, if I gaze at the ceiling above
the television picture and then suddenly flick my eyes downwards to the
floor, I see the picture momentarily upside down. The horizontal lines of
a television picture are rapidly created in succession one below the other
and if my gaze happens to flick downwards at nearly the same rate then all
the lines will be seen at nearly the same level on the retina, and the picture
will be shortened vertically. It may even degenerate into a single horizontal
line. Furthermore, if the gaze drops rapidly, the early lines at the top
of the picture are registered in the retina near the bottom of the visual
field and the later lines appear near the top, so that the picture is seen
upside down. John Little Glasgow