I picked up some really good apple branches from a bird lover lady, very nice chat we had too! She helped me choose the more "fun" branches.
One of them is definitely lighter in weight than the others, and a closer look showed that the core of the branch is hollow, there is a hole of about 1/2 inch.
Is it a sign of disease? Or just that that particular branch was old and dying?
They other branches are extremely healthy, been cut 10 days ago so still nice and green.
Loads of gem-looking things, can I keep them on when I hang the branch in the bird room?

Does the hollow branch look like it's basically healthy? If it's healthy-looking and has been cleaned I wouldn't worry about it. It probably got damaged somehow and lost the inner core.

I don't know what the gem-looking things are, can you post a picture?

They are still in the car, I will post the pic as soon as I get them upstairs tomorrow.
The hollow branch looks dead, compared to the others. They are all very flexible, that one is brittle. I will post that too.
Thank you Tielfan!

If the branches don't look healthy don't
use them.. you can never be to careful...
Im wondering what the gem looking things are?

Today I woke up with toothache again so my day was spent trying to move my head the least possible and reciting the mantra "it's just pain, ignore it". so I am sorry but the branches are still in the car and I took no pics, but I will do it tomorrow because, toothache or not, I need to unload the car to go get some ash branches.
Sorry about it

It sounds like your birds have you working full time to collect branches for them lol.

how's the tooth ache?
You going to visit the dentist?
Would help with the pain..

It comes and goes, thank you for asking, Jan. I hate dentists but tomorrow I will make an appointment.

I took the pictures a last.

This is the core:




I was wrong about that particular branch looking dead, it has a lot of gems and looks very alive, maybe it just looks a little bit lighter in colour, compared to the others.

this is how the wood looks in that branch




and this is the entire branch



sorry about the toilet bowl in full view lol

Good way to toilet train your birds! Now all you have to do is get them to flush. Just kidding of course, an open toilet is hazardous for birds.

The branches look fine to me and I wouldn't be afraid to use them if that's what these trees typically look like. A branch that died naturally before you collected it is going to be more brittle than one that was fresh when you cut it, and if it's not strong enough to do the job that would be a good reason to throw it out. But otherwise I don't think it should be a problem.

This is a pic of the other branches, they look a bit darker




The circled ones are a few of those I called "gems"