Invite students to discuss the ideas of sets of items that belong together. While three items may share a characteristic or belong to the same group, a fourth item may not share that same characteristic. Or that fourth item may belong to a different group. Provide an example of this, such as shark, whale, dolphin, horse. Discuss which three share a characteristic. To what group could three of these animals belong? Which animal does not belong (or could be called the “Odd One Out”)? Why?