I have never actually seen one. I could just feel their presence sometimes. Once, I was still studying at college. Well, college students, always late night sleep.
One night, while I was doing my assignment, and it was about 2am, I realised that something was behind me, and looking at me. My computer was placed at the corner of my dining area. Therefore, I was actually facing the wall. Out of blue, I felt something brushed through my right hand and instinctly, I looked behind. There was a cat looking at me attentively. I was blank for a couple of seconds and decided I should just go to sleep. I chased the cat out and went upstair to my room.
As I went into my room and about to enter the toilet, the toilet door was actually shaking, as if someone was trying to open the door but it's lock. I even put my hand on the door to feel the shaking, just to make sure that I was not imagining things.
Regrettably, I didn't open the door and went to sleep straightaway, while the door was still shaking. I felt asleep almost instantly only to be woken up by a dream where I actually opened the toilet door and something scared the hell out of me which made me jumped up from my bed!