Whenever I see my cats focused on something, it's a signal to me that's there's something they're hunting. That's how they let us know there was a snake in the house a few years back - another story for another time. (Actually, there have been snakes in the house on three separate occasions.)
This is an example of what that looks like:
On this particular night, they were hunting a baby gecko. The fact that it was a baby did not prevent me from screaming when I saw it. I couldn't wait for Wayne to come rescue me from the monstrous baby gecko because the cats would have mauled the poor thing, and the next step would have been eating it!
I grabbed a paper towel and used it to grab the baby gecko and throw it outside. Live, baby gecko! And don't come back in the house!