The artist drew the shell uses a woody pattern and I associated the word woody with hard. The artist also drew lines on the inside of each plate of shell, and I imagine that these would be the shell's ridges, making it bumpy.
This is so cute. Looks like mixed media of paint was used in this piece. Nice thick brush strokes to make this. This has a unique style. Love the tigers big eyes, also a chinese symbol added above his head.