You can try carving peach pits. The above ones I did with an "exacto" knife. Just a razor blade. Used some floor varnish that was kicking around. Some sanding went into them too.
The peach pits should be well cleaned. Usually you have to use some scrubbing to get off the peach fibres that cling. Dry it off. It's ready to go. Two other things: you will at some point need to take out the actual seed within the pit. For instance, with the bearded face above, on the flipside of it I took out with a small fine toothed saw just a wide enough section so I could get inside it with any small instrument and remove, either in small or large pieces, the seed inside. You should wash your hands after you do this, as the seed contains arsenic, or cyanide, or something very poisonous. The other thing: when you are carving, be careful. Because you're having to hold onto that small thing with your other hand...well, you can imagine the sudden slices you will give yourself with that razor knife, if it slips.
Carving these is actually quite smooth once you get the feel of it. It's basically wood, but without any grain. So yeah, quite pliable.