We hadn't figured out the exact hows yet, but we've seen it in action and found out how to make it work. When it was activated, it gave off a petri-beam in a widening sphere with the medusa at the center.

[He demonstrates a widening circle with his hands. He's more occupied with talking than eating more food at the moment.]

And to activate it, you had to say a distance in meters and a time. In English. The distance became the radius, and the time was how long you had before it went off. So you could set enough time to high-tail it out of there if you needed to.