Start with an empty yogurt container. I found the yoplait ones worked best since they have a narrower top.
Fill an old nylon with 1 TB grass seed and then fill with about 1 cup of potting soil. Tie a knot at the end of the soil (don't tie it lower or the dirt will fall down).
Fill the cup with some water and let end of nylon hang into it to soak up the water. Add some eyes and spray the top with water, keeping it damp. Eventually the grass will grow for hair (and maybe a mustache and beard!! It is fun to give them haircuts.