Burying objects in litter tray

I have 2 male kittens around 9 months old, one of them has developed a habit of burying objects in the litter tray. This usually happens over night but sometimes we catch him trying to do it during the day. It's usually socks that we find buried in there but can be other things like pieces of paper or carrier bags. We cant understand why he does it and how we can stop him from doing it!

Answer by Kate
Hi, sorry to say i have not come across this before, perhaps another vistor to our site will have come across tis before.

The only thing i can think is that your kitten is trying to hide things from the other cat and keep them for himself, perhaps he feels a little threatened and feels the need to protect his things.