Neutrinos they are very small.

They have no charge and have no mass
And do not interact at all.

Well, so said John Updike. They don't have no mass, but very very little mass, and it now appears that they have even less mass than people thought as you can read here. And while to them "The earth is just a silly ball," by detecting them deep underground you can learn quite about the Earth, which you can read about here. Enjoy, and my apologies for butchering that quite cute poem.