Each of the standard Tetris pieces have little animals in them. The square is a turtle, the 4x1 is a snake, and such. The pieces fall like normal Tetris, but when you clear a line, the animals get cut into pieces.
There were other things as well, a "shotgun" which blew a 2x2 hole in the pieces, then other pieces above would fall down. Also there were "pet rocks" which would fall, and smoosh down pieces that they landed upon.
Rob Reay and I designed most of the game, which only existed on a whiteboard in a house we were living in a few years ago. It was also to help us get into the groove to code up "Black Page," which we hadn't abandoned quite yet. I might have copied the information from the whiteboard, but I doubt I could find it at this point.