Possible Clues:

• Get the letters for the witches
• Amounts to
• What the witch deals with in her letters
• The magical way one deals with 21 across
• How one gets the letters that may be cast
• Indefinite periods
• Kisses may break them
• Adds up to
• Says 'D-O-G' or 'C-A-T,' e.g.
• Part of some Hogwarts classes