This story is from a book called "The Secret of the Crocodile", a Namibia Oral Tradition Project, published by New Namibia Books. (Paraphrased)
How the crocodile got its knobbly textured skin:
The crocodile originally had a smooth golden skin, and it stayed that way because the crocodile would spend all day in the muddy waters and only come out at night. All the other animals would come and admire it's beautiful golden skin. 
The crocodile became very proud of its skin and started coming out of the water to bask in the other animals' admiration, even while the sun was shining. He bagan thinking he was better than the other animals and started bossing them around. The other animals became bored with his change in attitude and fewer and fewer started showing up to look at his skin. But each day that the crocodile exposed his skin to the sun it would get uglier and bumpier and thicker, and was soon transformed into what looked like bulging armor. Crocodile never recovered from the humiliating shame and even today will disappear from view when others approach, with only his eyes and nostrils above the surface of the water.