For me, knock at the door.
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a human in demon cosplay jumping onto you...friends are fun..
Just going for a walk. I work nights and try to sleep days, really miss taking a stroll in daylight!
The random house noises. During the daytime it doesn't matter, but at night your brain is like "is that just the house settling, or did I just hear footsteps?"
I live in an old house (old by New Zealand standards anyway, since we're a young country) from the early 1900s. Overtime, I've gotten used to the walls creaking and when rodents decide to noisily run around in the walls, and in the crawlspace under the roof.
That one chair in the corner of your room with a mountain of clothes on it. At two am that thing looks like a person watching you sleep.
The sound of my cat eating a mouse in the dark on the veranda. Cool at 2pm, but at 2 amis really creepy until you turn the light on.
Tapping on the window. It turned out to be a giant moth during the early hours btw but, it freaked me out since I was watching a horror film which didn't help.