diff --git a/Common/src/main/java/at/petrak/hexcasting/api/misc/DiscoveryHandlers.java b/Common/src/main/java/at/petrak/hexcasting/api/misc/DiscoveryHandlers.java
index e9f3a98d..05f0cdcd 100644
--- a/Common/src/main/java/at/petrak/hexcasting/api/misc/DiscoveryHandlers.java
+++ b/Common/src/main/java/at/petrak/hexcasting/api/misc/DiscoveryHandlers.java
@@ -18,6 +18,7 @@ public class DiscoveryHandlers {
 	private static final List<Function<CastingHarness, List<ManaHolder>>> MANA_HOLDER_DISCOVERY = new ArrayList<>();
 	private static final List<ToFloatFunction<Player>> GRID_SCALE_MODIFIERS = new ArrayList<>();
 	private static final List<Function<CastingContext, List<ItemStack>>> ITEM_SLOT_DISCOVERER = new ArrayList<>();
+	private static final List<Function<CastingContext, List<ItemStack>>> OPERATIVE_SLOT_DISCOVERER = new ArrayList<>();
 
 	public static boolean hasLens(Player player) {
 		for (var predicate : HAS_LENS_PREDICATE) {
@@ -52,6 +53,14 @@ public class DiscoveryHandlers {
 		return stacks;
 	}
 
+	public static List<ItemStack> collectOperableSlots(CastingContext ctx) {
+		List<ItemStack> stacks = Lists.newArrayList();
+		for (var discoverer : OPERATIVE_SLOT_DISCOVERER) {
+			stacks.addAll(discoverer.apply(ctx));
+		}
+		return stacks;
+	}
+
 	public static void addLensPredicate(Predicate<Player> predicate) {
 		HAS_LENS_PREDICATE.add(predicate);
 	}
@@ -67,4 +76,8 @@ public class DiscoveryHandlers {
 	public static void addItemSlotDiscoverer(Function<CastingContext, List<ItemStack>> discoverer) {
 		ITEM_SLOT_DISCOVERER.add(discoverer);
 	}
+
+	public static void addOperativeSlotDiscoverer(Function<CastingContext, List<ItemStack>> discoverer) {
+		OPERATIVE_SLOT_DISCOVERER.add(discoverer);
+	}
 }
diff --git a/Common/src/main/java/at/petrak/hexcasting/api/spell/casting/CastingContext.kt b/Common/src/main/java/at/petrak/hexcasting/api/spell/casting/CastingContext.kt
index dbf8c267..0e0866bd 100644
--- a/Common/src/main/java/at/petrak/hexcasting/api/spell/casting/CastingContext.kt
+++ b/Common/src/main/java/at/petrak/hexcasting/api/spell/casting/CastingContext.kt
@@ -134,26 +134,12 @@ data class CastingContext(
     // for what purpose i cannot imagine
     // http://redditpublic.com/images/b/b2/Items_slot_number.png looks right
     // and offhand is 150 Inventory.java:464
-    // todo discovery?
-    fun getOperativeSlot(stackOK: Predicate<ItemStack>): Int? {
-        val otherHandStack = this.caster.getItemInHand(this.otherHand)
-        if (stackOK.test(otherHandStack)) {
-            return when (this.otherHand) {
-                InteractionHand.MAIN_HAND -> this.caster.inventory.selected
-                InteractionHand.OFF_HAND -> 150
-            }
-        }
-        val anchorSlot = when (this.castingHand) {
-            // slot to the right of the wand
-            InteractionHand.MAIN_HAND -> (this.caster.inventory.selected + 1) % 9
-            // first hotbar slot
-            InteractionHand.OFF_HAND -> 0
-        }
-        for (delta in 0 until 9) {
-            val slot = (anchorSlot + delta) % 9
-            val stack = this.caster.inventory.getItem(slot)
+    fun getOperativeSlot(stackOK: Predicate<ItemStack>): ItemStack? {
+        val operable = DiscoveryHandlers.collectOperableSlots(this)
+
+        for (stack in operable) {
             if (stackOK.test(stack)) {
-                return slot
+                return stack
             }
         }
         return null
@@ -167,11 +153,8 @@ data class CastingContext(
     fun withdrawItem(item: Item, count: Int, actuallyRemove: Boolean): Boolean {
         if (this.caster.isCreative) return true
 
-        val inv = this.caster.inventory
         // TODO: withdraw from ender chest given a specific ender charm?
-        val stacksToExamine = inv.items.toMutableList().apply { removeAt(inv.selected) }.asReversed().toMutableList()
-        stacksToExamine.addAll(inv.offhand)
-        stacksToExamine.add(inv.getSelected())
+        val stacksToExamine = DiscoveryHandlers.collectItemSlots(this)
 
         fun matches(stack: ItemStack): Boolean =
             !stack.isEmpty && stack.`is`(item)
@@ -226,6 +209,18 @@ data class CastingContext(
                     add(inv.getSelected())
                 }
             }
+
+            DiscoveryHandlers.addOperativeSlotDiscoverer {
+                val slots = mutableListOf<ItemStack>()
+                val anchorSlot = if (it.castingHand == InteractionHand.MAIN_HAND) (it.caster.inventory.selected + 1) % 9 else 0
+
+                slots.add(it.caster.getItemInHand(it.otherHand))
+                for (delta in 0 until 9) {
+                    val slot = (anchorSlot + delta) % 9
+                    slots.add(it.caster.inventory.getItem(slot))
+                }
+                slots
+            }
         }
     }
 }
diff --git a/Common/src/main/java/at/petrak/hexcasting/common/casting/operators/spells/OpPlaceBlock.kt b/Common/src/main/java/at/petrak/hexcasting/common/casting/operators/spells/OpPlaceBlock.kt
index e67e3e68..bd3758b0 100644
--- a/Common/src/main/java/at/petrak/hexcasting/common/casting/operators/spells/OpPlaceBlock.kt
+++ b/Common/src/main/java/at/petrak/hexcasting/common/casting/operators/spells/OpPlaceBlock.kt
@@ -63,9 +63,8 @@ object OpPlaceBlock : SpellOperator {
             )
 
             val bstate = ctx.world.getBlockState(pos)
-            val placeeSlot = ctx.getOperativeSlot { it.item is BlockItem }
-            if (placeeSlot != null) {
-                val placeeStack = ctx.caster.inventory.getItem(placeeSlot).copy()
+            val placeeStack = ctx.getOperativeSlot { it.item is BlockItem }?.copy()
+            if (placeeStack != null) {
                 if (!IXplatAbstractions.INSTANCE.isPlacingAllowed(ctx.world, pos, placeeStack, ctx.caster))
                     return