Socket on the left is fed in from the back and is separate from the right socket, then using a ‘widow maker’ supplies the circuit extending from the right socket but at the same feeds the standard lamp so that the paramedic can identify the cause of death -
Yeh, I haven’t a clue!
Yes.. Speakers! They are tie-lines from backstage to FOH that run through conduits and are terminated with 2A sockets at each end. It's actually mono, so the two plugs are simply wired in parallel to the amplifier output, which at 70W into 4 ohms cannot deliver hazardous voltages to the plug pins. 2A is not used for anything else that they could be confused with, so it's perfectly OK. Installed around 1971 I suspect.