Neutrinos are extremely small particles that are produced by nuclear reactions. The crazy thing about them is that they barely interact with normal matter, like automobiles, dentists, or enchiladas. They're so weakly interacting that if you shot one through a lightyear of lead, it would only have a 50% chance of hitting anything along the way. Compare this to photons, which are what light is made out of. They're easily stopped by construction paper (and dentists).
Recently, physicists have theorized that out of all of the elemental particles that exist in the Universe, neutrinos are the most child-safe. Neutrinos also have a reputation for not being very fun at parties.
The nuclear fusion reactions in the Sun generate a huge number of neutrinos that are flying straight through the Earth all the time. The Sun generates so many neutrinos that one hundred billion of them pass through each of your fingernails every second.
Scientists detect neutrinos using tanks filled with fifty thousand tons of water, located one kilometer underground, to avoid interference. In the extremely rare event that one of the neutrinos flying through the tank hits one of the water molecules dead on, sensors on the walls of the tank register a very dim flash of light.
Every second, one billion billion neutrinos fly through the tank. The tank has roughly one hundred million billion billion water molecules in it. Despite the overwhelming odds, it is necessary to hire specially trained, extremely patient scientists to wait around for almost two hours before a single neutrino will hit one of the water molecules. During this period, the scientists will typically play poker or watch embarrassing YouTube videos of other scientists.