question about egg health

I am about 28 days in incubation and am currently incubating 2 "boob eggs"
My question is when I candled them at 21 days I could see a little movement in the egg. At 28 days I can see movement in 1 but not much in the other but it still has healthy veins. I guess the question would be if an egg goes bad would the veins still be present or do they not move quite as much the farther along they go?

If you candle after the egg has died it will look like the veins kind of exploded. If you see good veins it's still alive.

By that do you mean the veins will be thicker of will there be some other sign inside the egg? Also if it dies how long does it take before the egg changes appearance. Thanks again

It looks like the veins just shattered....

They fall apart and dont resemble your typical veins.

There's breaks and blotches, instead of continuous "veins"

Thanks for the help. So far so good. Both appear to be doing ok. This wait is killing me!