The bakelite or plastic light fitting which was attached to the electrical cable which ran between tents or temporary installations. It had 2 sharp contacts which pierced the insulation of the cable.

a minor annoyance

A tiny bubble, literally about the size of a pinprick, in the ceramic from firing, and underneath the glaze, though it can appear to be right through it as the glaze may not have taken over the pinprick. Minor fault.

small puncture (as if made by a pin)