This is the first time that Piper's power of "Molecular Combustion" is used. She blows up a clock waiting in line at the courthouse. Leo explains this as, "Piper's powers work by slowing down molecules, and apparently now she can speed them up as well."
When Phoebe hugs Janna she doesn't wrap both arms because her right arm is still covered in the salve and her gratitude extends to preserving Janna's shirt from getting messy or stained