clarify preservation spells

spells.tex

@@ -222,8 +222,7 @@ A good witch leaves no part of her prey unused.
   The target ceases all rotting when not in use.
   Rain or snow may fall upon it, but it will not degrade}% Description
   {
-    Anyone working with the undead must make use of this spell.
-    To work without it means any undead creatures summoned will not last long.
+    Without this spell, any undead creatures would rot ever faster than a corpse in the ground.
 
     The spell degrades when the target begins moving, and fails within \arabic{spellPlusOne} \glspl{interval}.
     Therefore, undead spellcasters, such as liches, must continuously cast this spell upon themselves.