Hi [first time posting here]

My cat has an interesting and cute obsession.

First, his name is Baggy and he is a very healthy neutered 13 year old
pure black shorthair.
He is a well adjusted, friendly cat that loves to be picked up by me.
There are 4 of us here but he only really wants to be held by me.

For the last 2 years or so, he picked up this weird habit. We have
this little juggling ball that much resembles a hackey-sack ball. At
night when we are upstairs in bed he soon follows with the ball in his
mouth, howling the whole time. Once upstairs, he drops the ball and
totally ignores it after that. He completely ignores the ball at all
times except when he is carrying it. If I toss the ball back
downstairs, he won't chase it, but he will bring it back up sometime
during the night. On a weekend we sometimes stay up late watching a
movie downstairs. On those nights, he will bring the ball back
downstairs. He seems obsessed with keeping that ball near us but only
at night. The ball has never had any meaning to him, at least as far
as we can tell.  He has always totally ignored it except when he was
carrying it.
It's quite harmless and amusing, so I am simply curious as to what he
is thinking. Any ideas?

Thanx in advance.