This is a great lesson that I've done for years- I found it here on the United Art & Education website:
Students choose an African animal, then draw it on heavy white paper in pencil first. The, using an applicator of your choice, (Q-tip, end of a paintbrush, brush, bamboo stick, etc) have students go over the pencil lines with black glue (white glue with india ink or black paint mixed in). Using something other than a pen forces students to 'loosen up' a bit and also gives a nice line variety. Let dry overnight, then students paint it (doesn't have to be realistic) with watercolours or ink. I do a demo of a wet-on-wet technique, mixing analagous colours, or using only warm or only cool colours.
We used ink for these examples.