I was taking a not usual wing to wing apartment stroller drive when I heard a sound, not an ordinary always seen and commonly classified sound. It wasn't like a howl, shriek, screech, broadcast, alert or stomping and rumbling earthquake type. It was more like a mythical creature belonging to any mythos like the cthulu mythos, it was like a roar but in a really pitch tone with a metalic scrape type of screech which groups into at least seven sound waves. I checked the halls and found some black, contorted and sound reflecting goo which moved along the hall floor. It slid out a small window and I heard an explosion and checked that very window but then there was a big explosive hole or dent an its radius was high, I never heard that sound again nor seen an explosive goo.