Surely this perceptions happen on a mental dimension. But that something happens on a mental dimension not implies that it would be simply a fantasy, a fantasy is a mental fact that happens in only one mind at the same time. But what will happen if that exact ( not only similar) fantasy will happen in 2 or 3 brains at the same time.
I wonder, too? As have posted here loads before, stepsister and I both saw the exact same thing. We know it was the same week. Because it was during a week they stayed at our house before our parents married and although the future steps visited several times before my dad married her mum, that was the only time she and I shared that certain room. But I never told her what I saw (she was asleep when I saw it) and she didn't tell me what she saw til we went out for a meal together 15 years later. My husband had heard me recount this many times before my stepsister spoke, so he nearly fainted as she recounted seeing what I had seen, too, all those years before.
We were two unhappy little girls, both recently bereaved, she was being dragged from the only home she'd ever known and we were having to get used to the idea of our home never being our own again. So it's classic, in that way - right gender, right age, and both traumatised kids.
I never told her what I saw or even hinted at it as she was a stranger and I thought she'd think I was nuts. She never told me for the exact same reason.
Why did we see the same thing in the same room? (Possibly not on the same night - we shared that room for a week, IIRC).
Should add, the house was badly haunted and I knew it, had known it my whole life. It was Borley Rectory levels. She didn't know it as nobody had told her. So not sure expectations play a part.
But this is what I struggle with. Generally I'd assume thought forms but... what are the mathematical odds two (then) strangers would see the same thing?
Should add: her story was identical to mine in terms of the fine details. Everything the same. I thought she was asleep when I saw it and she thought I was asleep when she saw it. It was closer to me than her but raised a couple of foot above floor level so she'd have seen it about as well as I did (next day when I told my dad, when none of the steps were around, he said he had indeed changed the floor level of that room before I was born, and it was originally a couple of feet higher - in retrospect I realised that detail was maybe why he believed me when I said I'd seen a ghost - he took it in his stride when I told him).
When we became stepsisters, we didn't get on - nobody's fault - two grieving kids only days apart in age and with diametrically opposite personalities and interests. So we had no mutual friends or even acquaintances. We went to a huge school and were a year apart, because my birthday fell just after the cut off date for that, her's just before. So anyone either of us ever told about it will never have spoken to anyone who was friends with the other. We had nothing to do with eachother. I wouldn't even eat in the same room as them unless forced. I never told my stepmother what I'd seen and she never told my dad. My dad was very sceptical re ghosts (or pretended to be) so he wouldn't have mentioned it to my very christian and easily offended stepmother. So I think there were no conduits through which either of us could have known what the other saw.