Ice rocks the size of a dog's head falling from the sky are nature's way of telling you to go inside.
You should really have somebody take a look at that. (Via Live Storm Media YouTube)
Spencer Basoco and Lawrence McEwen are stormchasers, which is a bit of a misnomer since the activity isn't really about observing or following storms so much as it is getting caught inside of storms. Last weekend, they were following a storm outside of Stephenville, Texas, when the storm followed them and rained unholy hailfire onto their vehicle. This wasn't regular hail, this was gigantic, rock-like, end-of-the-world hail. The stormchasers described the hailstones alternately as "grapefruit" and "softball"-sized, depending on if you like your terrifying metaphors food- or sports-based.
Check out their harrowing first-person video of the hailstorm, and their search for cover: