Fire is more worrying. You can also make small sparks with 5 volts under certain conditions, which may frighten someone about as much as a small shock.
There were no loose energized cable ends in this story, fyi. The light strip was your standard white LED tape cut in the middle of the copper pads [0]. I soldered the USB cable's power leads to the copper pads [1] and then covered the solder joint with heat shrink tubing filled with liquid electrical tape [2]. Then on the strip I connected to, it was the same procedure but with a female USB-A connector. There were no conductors with exposed ends to move apart and make a spark.
