No witches were ever burned in Salem as shown in the opening flashback sequence set in Salem, 1692. The 18 people executed there died by hanging and a 19th person was crushed to death by stones.
The first time that a warlock exhibits the power of blinking or instantly teleporting between places.
This is the first episode that Phoebe has a premonition about the past.
When Prue leaves for the museum, she drives a car that was totaled back in the Dream Sorcerer (1998) when she crashed into a pole.