Black circle nose cones on BA are on the B757s. Why? No idea!!
IFE system and cabin electrics cut out on engine start up, the lights may go off then on and its actually the seatbelt signs/ no smoking signs you hear coming back on. Its like if you have your lights on in your car and start the engine, they dim. This can happen when switching from ground to aircraft power.
The same thing may happen when engines are switched off, you can lose cabin lighting and sign illuminations. This is when the aircraft switches from its own power supply (APU) to the supply from the ground (GPU).
Left hand passenger doors are bigger than the right hand ones which are used for servicing the aircraft (catering,cargo,etc). Also jetbridges worldwide are angled to fit to the doors on the left, if they were for both sides it would take longer, be more tricky to manouvre and would cost more to manufacture. If pax boarded from both sides, the cargo, catering, water and fuel vehicles would be dodging around on the ground, and may cause delays or are more likely to collide with pax steps, etc. (well thats my theory!)