Example? A magnetic field alone does not affect an electromagnetic wave.
With regard to slowing light, is this what you refer to?
Throw in my tuppence:
one of the reasons people have difficulty with relativity is that one intuitively feels that length and time are some special invarients that never change. However, when one works out how one actually measures them, you find they are indirectly and directly tied to the speed of light. For instance, a simple ruler might be the distance between two atoms tied in a bond (a real 12" ruler is just multiplied many trillion times). The atoms are held apart by electrostatic charges that propagate at the speed of light. Similarly a simple clock might be based on the time it takes the two atoms to vibrate once. Again the forces that control this propagate at the speed of light.
So in an extremely nonquantitative way, it can be seen that it is not unlikely that our measurements of length and time are influenced by the speed of light, and even by relative motion.
Take an ordinary 12" ruler moving away from you. The light from the far end that is hitting your eye at the same time as the light from the near end started earlier when the ruler was closer to you. The ruler thus appears shorter.
It’s all a consequence of the finite speed of light. If light traveled at infinite velocity, whatever that means, we wouldn’t have this nonsense.
If this explanation were correct than a 12" ruler moving toward you would appear longer. However, this is NOT what is predicted by special relativity. Moving rulers appear ALWAYS appear shorter, even if they are moving toward you.
I know, I came to the same conclusion not too long ago. :smack:
But I was too fast for ya! 
It’s so easy to make mistakes talking about relativity. Everything about it is so counterintuitive … .
This illustrates a very important point about relativity. Time dilation, length contraction etc. have nothing to do with light travel time delays. You have to imagine a space filled with an infinite number of synchronized clocks and distance measuring devices. When an event occurs you go to these devices and read off the recorded times and distances involved. It’s not what you see it’s what actually is.
Echoing what Ring said: If you get the same effect with bullets instead of light rays, it’s not special relativity.
Well, the problem is that when you have accelerating reference frames the reasoning doesn’t go through anymore. General relativity was invented to cope with that.
Eh, you can deal with accelerations in Special Relativity. And when the changes in speed are instantaneous, or close to it, as is usually the case in the Twin Paradox problem, it’s easy to deal with it in SR. The trick is that you can’t just assign a single reference frame to the rocketship: You need at least two, since the rocket travels at two different velocities (one moving away from Earth, and one returning). You can, however, assign a single reference frame to the Earth. You can do all of your calculations in any one of these three reference frames (or indeed any other reference frame at all, though you might not want to), and you’d get the same answer. But you can’t work in “the rocket’s reference frame”, since there is no such single frame.
Yeah, you can jury-rig something to work, but it gets more and more onerous to do so until you throw up your hands and invent general relativity just to get it over with. It’s sort of like the changeover from the epicycle model for orbits to the elliptical model.