This is a very stupid question, but can you tell me how I accidentally just took a screenshot on my Samsung Galaxy S4?

I was trying to do something, and being impatient, I started sort of “smashing buttons” on my screen, and before I knew it, I had taken a screenshot. I know you can do it by holding the power and menu button, but I didn’t touch any buttons this time. I’m interested to know what I may have done so that I may do it again in the future.

Can you tell me what other method there is besides using those buttons?

I would Google it, but I’m at work and the internet here is growing increasingly frustrating and most of the results don’t work.