Is it normal to have these kinda thoughts?

Sometimes, when I'm really bored, thoughts would just randomly pop in my head and they're usually quite disturbing.

Today, I went to the train station and it was crowded at the platform area. There was this short lady in front of me and every now and then, she would crane her neck to see if the train was approaching. When I heard the train approaching, I don't know why, but I had this mental image of kicking her off the platform and her getting run over by the train.

I read an article online and according to that article, such thoughts are called "intrusive thoughts". I don't have them all the time, and I don't know what triggers them.

Here are some intrusive thoughts I'm not proud I had:

- Nice house! I wonder if it would still look nice if I set it on fire?
- The server's coming this way. I should extend my legs so that he trips over them.
- (When my niece was still a baby) I should drop her down the stairs and see what happens.
- Should I follow her to her house to see if she lives alone?
- (While holding a knife) I should stab my brother in the throat just to know what it feels like stabbing someone.
- I want to pour boiling hot water on my dog.

I know they're disturbing! I would never act on any of them. To be honest though, when I have these kinds of thoughts, I find them absolutely hilarious that I'd start giggling to myself like the psycho I am inside.