can anyone help me in the snake mound(?)puzzle? I don't know what I'm supposed to do with those plates and that rod

If you examine the tiles, each of them has a different number of lines (1, 2, 3 and so on up to 12). You have to put them in their place in ascending order (there are two tiles with a fixed position which helps you determine the correct order). After you put them back, you have to use the rod in the hole in the center of one of the tiles (I forgot which one, so try them until... well you'll know when you found the right one). :)

Remember the German expression that helped you solve the clock puzzle in Grandma's house? That expression is relevant once again. If you read the book on snakes in the book shop, Grace should have told you an important tidbit about snakes.