Hysteria is defined as exaggerated or uncontrollable emotion, especially affecting a group of people. For example, the accusations of the girls — as well as the Putnams', Parris', and Hale's willingness to believe them — ignite a hysteria in Salem Village. Some of the girls themselves appear to succumb to hysteria, girls like Mary Warren, who seem so caught up in uncontrollable emotion that they can actually grow physically cold and even faint whenever emotions run particularly high. It's only later that Mary realizes that she didn't actually feel the results of witchcraft but of hysteria (though she does not call it this). Peer pressure also plays a role in hysteria; it is, simply, influence from one's peers. Mary certainly experiences this — she is unable to recreate the sensation of growing cold or fainting without the group doing it as well. The more people grow to believe in the accusations, that there are witches loose in Salem Village, the more it seems to compel others to believe as well so that, soon, it becomes possible for people like Rebecca Nurse or John Proctor to be hanged.