Note: I played it in browser, maybe I had some performance problems due to this, even other games do run smoothly.
With stiff I mean: clicking on the icons below did not feel responsive/ immediate PLUS having to click first on icon, then on the field, then back on the icon, then on field are a lot of mouse movements (I think something like a context menu/ icons appearing at field clicked then choose one action). But is just my very subjective feeling.