What would make a 10 year old cat suddenly start chasing and biting it's tail?

Question

He is neutered and hasn't done this since he was a kitten

Answer 1

He might have parasites. Get him to a vet.

Answer 2

if you live in australia then it's because spring time is coming up and all animals go crazy in spring.

try to keep him away from birds,

and make the most of it, play with him. :)

Answer 3

I don't know....

I think you should try taking him to a vet if you start to worry.