This is a kind of "X files" thread.
Post experiences which spooked you, which made you doubt reality, mathematical or physical laws, your sanity, memory or perception. The more improbable the better, but no second-hand legends please, share only what you personally experienced. If you had the event later explained rationally please use rot13 to avoid spoilers.
No, I was never able to repeat that experiment. However:
Zl fgebatrfg ulcbgurfvf vf gung gur pnoyr unq n gval culfvpny qrsrpg, juvpu pnhfrq ovg reebef zber bsgra jura orag "whfg gur evtug jnl". Vg pbhyq or grfgrq ol ybbxvat ng gur engr bs GPC/VC ergenafzvffvbaf pnhfrq ol vainyvq cnpxrg purpxfhzf, juvpu jr qvqa'g gubhtug bs ng gur gvzr. Guvf vf fgvyy ener rabhtu gung V qba'g rkcrpg gb frr vg ntnva, rira vs V unq gur rknpg fnzr pnoyr gb rkcrevzrag jvgu. Guhf gur gehr pnhfr erznvaf haxabja.
Edit: phase of the moon bug
That was my guess as well, except with "plug" instead of "cable".