The bad smelling yellow liquid is produced by the cells just under the outer rind. Like the sap of some trees, this liquid seals any wounds the plant might suffer.
The inner liquid should be clear and have little if any odor. Once you have removed the leaf from the plant, you can split it lengthwise to obtain this inner liquid.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams