From the introduction:
The derro and his ogres remain quiet until the characters actually break through the teeth and engage the bad guys in battle.
...
With one last hack, you forge your way through the ivory wall. The chamber beyond is about 20 feet high and very strange. It is hot, humid, and dank. The floor is a spongy, slimy surface that is has a pinkish, gray hue. The walls are a similar color, but there are bluish veins streaking the surface. Here and there are spots that look like scabbed sores—for a lack of a better term.
Of more importance, however, are the two ogres wielding morningstars and wearing half plate armor with shields. A dwarven looking creature stands behind them cackling in a maniacal manner. Before you can react, the dwarf chants and slashes his arm with his dagger. His blood sprays forth and magically leaps to floor at your feet. It is suddenly very slippery!
User summary:
The Heart of the Beast is provided as a 15-page PDF scenario and a 2-page DOC errata; with an additional 2-page DOC handout (print-and-play).