What "unusual behaviors" were the girls in Salem exhibiting?

The behavior of the girls accused of witchcraft in Salem was very strange indeed. No one had ever seen anything quite like it. The girls would scream blasphemous insults against God—scandalous to the deeply religious Puritan townsfolk—as well as falling into trances and shaking their whole bodies in convulsive seizures. All manner of natural explanations have been put forward to explain the girls' behavior, but at that time and in that place, the near-universal consensus was that they'd been possessed by the Devil.
Medical science in those days wasn't very advanced so the local doctors weren't able to determine a natural cause for this sudden outbreak of strange behavior. Like just about everyone else in town, they concluded that the girls were in the grip of dark, demonic powers that threatened to spread like wildfire throughout Salem unless firm action were taken by the authorities. This meant identifying witches—thought to be in league with Satan—and punishing them severely.