Prue and Piper discuss the fact that Piper didn't accidentally blow Prue up. At this point it has been well established that Piper can't freeze Prue and Phoebe because her powers don't work on them. If she can't freeze them, then she shouldn't be able to blow them up either.
After Janna puts the potion on Phoebe's arm in alternating shots her arm goes from having the potion to being red and scratched.
From 22:30 to 23:00, different characters are thrown against a large rock in a fight. The "rock" visibly moves, as if its not really a rock.