Laptop mouse touchpad thingie... zooming in and out by scrolling?

Sometimes when I think I’m just scrolling around, all of a sudden, I’m zooming in or out on what I’m looking at. I have no idea how I’ve made the mouse do it, nor do I know how I make it stop… I just… do it. Very annoying, as it happens quite a bit.

I know each model of laptop is different, but in general, how does one usually go into “zoom mode” so to speak with the laptop touchpad?