Spooky orb spotted on the Grand Hall Gallery

I received another interesting sighting story this week from a visitor.

"Just seen your blog and thought I would pass on something I saw yesterday.

Now first of all, I am certainly not a ghost hunting fanatic, in fact nothing could have been further from my mind as we walked around the house. I was so awestruck by the craftsmanship I didn't consider anything creepy or anything. I don't even know where exactly we were, but it was upstairs on the second floor of the main house. I THINK it was close to where you can look down into the main part where the greeters stand. There was a window on my left but definitely a big dark door at the end of the hall. I know the door was there for sure because it was against this dark backdrop that I saw what I saw.

I looked up and saw what I thought was an orb floating and darting for a few seconds in front of the door. It was fairly soft yellow and orange colour and I would say 1 cm . What struck me was first of all the size. This orb seemed to have a definite strong presence, was yellowy orange  and much bigger than a dust spec. It seemed to want to make its presence known and was certainly not shrinking into the background. I then dissuaded myself saying first of all it was probably a fly, but secondly that I wasn't even sure if orbs can be seen with the naked eye. Anyway, I was thinking about it today and I know for sure it wasn't a fly because  well it just wasn't and I have seen a couple of google posts to say that some people do see orbs with the naked eye. So I don't know exactly where I was in the castle but I know what I saw. I am finding Penrhyn FASCINATING though. Of all the National Trust properties we have visited, I find this one the most intriguing."

I have put photos on here of orbs on the Grand Staircase. I wonder what they are? I would be interested in any comments.