We were talking about cashews the other day, and most people had no idea that they look like this on the tree.
I remembered that the shell is poisonous, but I’d forgotten the details. When I looked for details on Wikipedia, I found that it’s related to one of my least favorite plants – poison ivy:
Like poison ivy, cashew shells contain urushiol, and need to be handled with extreme care until they’ve been roasted. Pistachios also contain some urushiol, which probably explains why you can have an allergic reaction if you eat too many of them.