Bosons and fermions are subatomic particles (bits of matter smaller than an atom). The difference between a boson and a fermion is the number of the atom's electrons, neutrons and/or protons. An atom is composed of bosons if it has an even number of electrons. An atom is composed of fermions if it has an odd number of electrons, neutrons and protons. An example of a boson would be a gluon. An example of a fermion would be potassium-40, which is what Deborah Jin used as the gas cloud. Bosons can form clumps and are attracted to each other, whereas fermions do not form clumps. Fermions are usually found in straight strings because they repel each other. This is because fermions obey the Pauli exclusion principle, which states that they cannot gather together in the same quantum state.