That is debatable. :evil:
That (static electricity) is what I thought. With a quick search, I did find something at HF on it but didn't know whether to trust the OP.
http://www.head-fi.org/t/310723/fyi-basic-guide-to-in-ear-canalphones-rev-4
"10. Static Electricity Discharge through IEM
It is possible to experience a static electricity discharge though IEMs.
In a cold climate with low humidity, a static charge may build up on
one's body. The cable that carries the audio signal from the headphone
jack to the IEM has metallic wire inside. This wire is also a path to
ground through which the static charge can travel. Though one's ears
are touching the plastic parts of the IEM, there is metallic wire
inside. A static charge often has a high enough voltage to leap from
one's ear to the metal inside of the IEM, discharging the static
electricity via the cable and into the device playing the audio
signal, e.g., CD player or MP3 player. The amount of electrical
current in such a static discharge is not harmful, though the
discharge itself can be startling.
It is important to note that such static discharges are "acts of
nature" and do not indicate that one's IEMs are defective, nor will
the static discharge cause harm to the IEM. Note: If you are regularly
shocked by your headphone, it could indicate a leakage in the wiring.
You should contact the manufacturer for repair in such a case."