Those are instances in J's tales that leave me grasping for explanations. There are many, many more stories from J and his parents that are uncanny, but there is at least a justification for each of them, at least, ones that make sense to me. I'm by no means discrediting their experiences, but imagination is powerful, electronic recordings are susceptible to natural interference, and dogs do something bark at nothing because they're assholes.

It's only when every avenue has been explored that I will admit I don't know. And the next two are just that.

My friends and I used to do sleepovers a lot. I was lucky enough to have female friends and male friends and got to experience both kinds of sleepovers. The girl sleepovers involved a lot of chatting, a movie, popcorn and... boys. The boy sleepovers involved tents, dares, video games and cringe-worthy home movies where I luckily nipped a terrible acting career in the bud.

It was at one of these boys sleepovers with J and T that something "off" happened. Like I mentioned before, it isn't what happens that scares you, but what is left to be desired. Normally we'd camp outside in a tent but the weather had been bad and J's parents advised we stayed indoors. We must've only been around 11 or 12 at the time.

I don't honestly remember much of what we amused ourselves with that particular night, but it was most likely a video game or wandering around the crop fields until the sun set, doing nothing important at all. The reason I hardly seem to remember anything else that night is because of what happened in the early hours of the morning.

Back then the family owned a very loud and irritating novelty cuckoo clock, so I always knew what hour it was. It was between 2am and 3am, and T wakes us up from our sleeping places on the sofas and points to the wall.

"What's that?"

It was a white triangle of light about as big as my hand, shining just above my head. Initially we didn't think much of it, because we were sleeping in the front room where there was a television, DVD player, lamps, all that regular stuff. It did puzzle us a bit because everything was off and the curtains were closed.

All three of us got up in the middle of the night, sneaking around so that J's parents wouldn't come down. It wasn't that we were scared by that point, just... a little puzzled. It hadn't been there before, that was for sure, and there was no light source shining on that wall, or indeed any.

We assumed it had to be a reflection off something. But we tried to find what could be reflecting or concentrating any light and we found absolutely nothing. Even with three curious kids searching the whole room. That was when it started to get just a little eerie and I felt the weight of it in my stomach. What were we looking at?

We tried waving our arms in front of it, but we couldn't cast a shadow. We tried to block the triangle with a cushion and the triangle shone on that instead. We couldn't make it go away. We couldn't move it or dim it. We opened and closed the curtains and all that did was brighten the room with the gold glow of a distant street light. No moon. No car headlights. The doors were closed both ends of the room. All the electric devices in the room were off at the wall. There were no mirrors to reflect, vases to refract, leftover glasses of liquid... We could find nothing in the room at all that would be the source for the light.

Eventually we packed up our sleeping bags and moved back into the conservatory where we'd been playing video games. T wasn't keen on staying in the front room with the triangle illuminated on the wall, for fear it was something paranormal.

I don't know what I believe. I partly think we must've missed something when searching for what might have caused it, but I just can't fathom what. We tried everything conceivable. And what unnerves me the most about it is that twenty minutes or so later we ventured back in to check on it, and there was no evidence it had ever been there at all.

This one may seem easy to explain upon reading the title. But what if I told you the knocking wasn't inside the walls or on the door, but on a window?

On the upper storey.

Bear with me.

It was yet another sleepover, this time at my house. We must have been a little older this time, definitely approaching 13, because my brother was with us and we cruelly teased him for not yet hitting puberty. Nice, I know.

J, T, my brother and I slept in the spare room, which happened to be in the middle of an open plan house. It was directly leading onto the dining room, which had a large window facing the back garden.

A garden, I might add, that was flat, featureless and certainly had no trees.

It was approaching midnight, if I recall, because my parents had gone to bed hours ago. We were still up and joking around, probably prodding a lifetime of humiliation towards my little brother that he still occasionally brings up.

That's when we heard the knocking.

A definite rattling thud on a glass pane that stopped our sentences short.

The most terrifying thing was that it wasn't on the dining room window; it was upstairs. Directly above us. In my bedroom.

I stated plainly before that I haven't been a believer in the paranormal since I was young, so investigating the noise didn't perturb me. J, T and my brother were terrified though, and thought I was stupid and brave for even getting to my feet while this terrible knocking sound was going on.

It was an urgent, forceful , over and over, like the kind of knocking when somebody slams the side of their fist into the glass pane of a door, wanting to be let in from the rain.

It vibrated the air in the house, but regardless I crept upstairs to see what it was. My parents were still and silent and their bedroom light was off (I know what you're thinking, and it certainly wasn't!) and still the rattling continued. When I opened the door to my bedroom there was nothing.

The curtains were still open, but all I saw was the end of the garden where the shed was. No tree branches to knock against the glass. The television aerial was at the front of the house and therefore couldn't rattle in the wind. There were no loose cables. The cat was out. The window was closed. Nothing moved the other side of that glass to have made the sound it did.

Even after observing it, standing in my room investigating the noise, I finally left without answers. By then I was skittish. I was probably even scared, because I'd expected something very ordinary to have caused it, and we could have laughed about it and then resumed teasing my poor brother. But it didn't go like that. I couldn't find anything to satiate my need to know what was so urgently banging on the upstairs window.

To this day I don't know and it remains one of the most uncanny instances me and my friends lived through. I like to know why. It's in my nature. I like to know why the dinosaurs went extinct and I like to know how black holes collapse into existence, so for me not to know the answers to current, observable incidents haunts me as much as the feeling of when it happened.

I don't believe lightly, but there are definitely some things I can't explain.