optical illussion
The wings dont act as slides....the flaps need to be lowered to 40 as part of the evac C/L...so that the drop to the ground is reduced.
The overwing exit on the 737 is the one which causes most of the broken legs sustained in an evac.
BTW the airbus has overwing slides
Runway edge lights when viewed from behind an NG engine,can create the illussion of a steady flame inside the engine.