pointy things

This is my boys birthday cake...a Hot Wheeel. I made it.

I found these pointy things on the beach again...the first time I found them was along the east river in manhattan now I found some more in coney island, tried to find them on the internet and in books but I can not figure out if they are animal or vegetable....they look like little devils...or bull heads, it is hard to tell if they are seeds or egg pods, I wish I knew what they are.