I just noticed that FreeCAD sometimes seems to be using “backwards perspective”: the side of a part that is obscured by being on the opposite side from the camera is projected as larger rather than smaller. This is easy enough to achieve mathematically (you just reverse the test for distinguishing visible surfaces from invisible ones) and I understand that there are actually some physical lenses that achieve this in real life as well, sometimes used for machine-vision automted inspection systems.
It occurred to me that this is actually a potentially powerful UI technique for increasing the visibility of parts in CAD, since, with a wide enough viewing angle, you can see the part from nearly all sides at once. FreeCAD in particular is using a rather moderate viewing angle, so the effect is somewhat subtle, and it doesn’t seem to be happening all the time.