My personal idea is that unless you're dealing with a crazy religious alien believer, then a single "hallucination" in the brain has to be explained and somewhat taken more seriously if they never experience anything similar again in their lives.
I wouldn't discount misinterpretation and memory as possibly more likely than full "hallucinations". Sometimes we see something and aren't sure what we saw, then our memory further complicates the situation. Case in point, Tuesday morning's walk:
We were at the end of our walk, just starting up the last little climb where the road crests in front of us. Maybe 100 yards/~100m or less. To the right of the knoll, it rolls down into the neighbors yard, to the left, there is thick brush. As were heading towards the knoll, we see a critter at the top. Something like this, with red x the location:
My wife said: "That looks like Lucus", the neighbors big black Doberman. It was standing perpendicular to us, so looking straight at us. I thought it looked like Lucus to, with the long head. The sun was to the left in the photo, so he was basically a silhouette. But then I thought, that's a long way from home for Lucus, he would have come up his long driveway and then up the road that's behind the knoll, 5-600 yards/~m or more. And he's getting old.
Then the critter turned and was now in profile as it headed into the brush to the left. Both of us stopped walking and said, "Shit!, That looks like a mountain lion". But that would mean we both perceived the face to be much more cat-like, than dog-like in profile. Then we both commented that the tail was wrong, it was too short and stubby, but still bigger than Lucus' nearly non-existent tail. Bobcat? Seemed too big for that, we've had bobcats around occasionally. As we watched, it headed off into the brush to the left.
Now proceeding slowly, as that's the way home, we continued to look to the left and into the brush trying to figure out what we saw. As we got closer to the top of the knoll, the nearby neighbor's dog, Minni, came up from the right and barked at us, as she does. As I looked at her, I noticed she has a short stubby tail, like a bobcat, but a pointed face like a dog. Had we confabulated the cat-like face in profile for some reason? But she was over here to my right, in her yard and whatever we saw had just headed into the brush the opposite direction.
Now 2 days later, not only do we not know what we saw, we're not sure what we remember seeing. Was it dog-like head on and cat-like in profile? Both? Neither? I just don't know. We don't always perceive things correctly, even at the moment, and then our memories of perception becomes scrambled. I don't think it was a hallucination of some kind, we both saw and perceived something similar, but we're not sure what.
Lucus?
Maybe, but he was further from his home than he usually wonders, going to the left would have taken him further from home and we would have seen him making his way back home as we finished our walk. And as he was looking towards us, he normally would just wait for us to get to him. He's a sweetheart.
Mountain Lion?
Mountain Lions have a distinctive long tail, and we both remember this thing having a short stubby tail. An injured Mountain Lion is possible I suppose.
Bobcat?
I'm leaning that way. We've seen them before at our place. Maybe the angle, with the cat being at the top of the knoll make us perceive it bigger than it was. But it would mean we miss-perceived the snout when it was facing us and we thought it might be Lucus.
One other possibility, is the other dog, Minni. Perhaps we saw her at the crest of the knoll, and for whatever reason, she went into the brush, away from home, then circled back to her own yard on the back side of the knoll out of site to us. As we (in blue) looked to the left, she (in red) had come around and up from the right:
Honestly, we're not sure what it was. It's just the way our brains work, they're not like film or digital recording devices. They often use shortcuts to interpret the visual information that comes in. We don't see, like a camera, we perceive. If at first, the critter resembled Lucus, our brains took a short-cut and filled in Lucus on the knoll. As it turned, our brains were forced to rework that. Not Lucus, but maybe still perceived as the size of Lucus. A cat-like profile the size of doberman equals a mountain lion. Then our brains perceive that the tail doesn't match our notion of a mountain lion, so it starts to fill in bobcat, but still perceived as the size of Lucus. Then the memory of all that gets even more convoluted.
