Fixes #9913

Also axes hidden var in lieu of using implants like other foreign objects. Now instead of one object, amount of stuff you can put in someone's organ is restricted by stuff's combined w_class.

code/modules/mob/living/silicon/pai/pai.dm

@@ -281,8 +281,9 @@
 		if(ishuman(holder))
 			var/mob/living/carbon/human/H = holder
 			for(var/obj/item/organ/external/affecting in H.organs)
-				if(affecting.hidden == card)
+				if(card in affecting.implants)
 					affecting.take_damage(rand(30,50))
+					affecting.implants -= card
 					H.visible_message("<span class='danger'>\The [src] explodes out of \the [H]'s [affecting.name] in shower of gore!</span>")
 					break
 		holder.drop_from_inventory(card)

code/modules/organs/organ_external.dm

@@ -39,7 +39,6 @@
 	var/cavity = 0
 	var/sabotaged = 0 // If a prosthetic limb is emagged, it will detonate when it fails.
 	var/encased       // Needs to be opened with a saw to access the organs.
-	var/obj/item/hidden = null
 	var/list/implants = list()
 	var/wound_update_accuracy = 1 	// how often wounds should be updated, a higher number means less often
 	var/joint = "joint"   // Descriptive string used in dislocation.

code/modules/surgery/implant.dm

@@ -45,7 +45,7 @@
 	can_use(mob/living/user, mob/living/carbon/human/target, target_zone, obj/item/tool)
 		if(..())
 			var/obj/item/organ/external/affected = target.get_organ(target_zone)
-			return affected && !affected.cavity && !affected.hidden
+			return affected && !affected.cavity
 
 	begin_step(mob/user, mob/living/carbon/human/target, target_zone, obj/item/tool)
 		var/obj/item/organ/external/affected = target.get_organ(target_zone)
@@ -112,7 +112,15 @@
 	can_use(mob/living/user, mob/living/carbon/human/target, target_zone, obj/item/tool)
 		if(..())
 			var/obj/item/organ/external/affected = target.get_organ(target_zone)
-			return affected && !istype(user,/mob/living/silicon/robot) && !affected.hidden && affected.cavity && tool.w_class <= get_max_wclass(affected)
+			if(istype(user,/mob/living/silicon/robot))
+				return
+			if(affected && affected.cavity)
+				var/total_volume = tool.w_class
+				for(var/obj/item/I in affected.implants)
+					if(istype(I,/obj/item/weapon/implant))
+						continue
+					total_volume += I.w_class
+				return total_volume <= get_max_wclass(affected)
 
 	begin_step(mob/user, mob/living/carbon/human/target, target_zone, obj/item/tool)
 		var/obj/item/organ/external/affected = target.get_organ(target_zone)
@@ -132,8 +140,8 @@
 			affected.wounds += I
 			affected.owner.custom_pain("You feel something rip in your [affected.name]!", 1)
 		user.drop_item()
-		affected.hidden = tool
-		tool.loc = target
+		affected.implants += tool
+		tool.loc = affected
 		affected.cavity = 0
 
 	fail_step(mob/living/user, mob/living/carbon/human/target, target_zone, obj/item/tool)
@@ -174,7 +182,7 @@
 
 		if (affected.implants.len)
 
-			var/obj/item/obj = affected.implants[1]
+			var/obj/item/obj = pick(affected.implants)
 
 			if(istype(obj,/obj/item/weapon/implant))
 				var/obj/item/weapon/implant/imp = obj
@@ -201,6 +209,8 @@
 					worm.leave_host()
 				else
 					obj.loc = get_turf(target)
+					obj.add_blood(target)
+					obj.update_icon()
 					if(istype(obj,/obj/item/weapon/implant))
 						var/obj/item/weapon/implant/imp = obj
 						imp.imp_in = null
@@ -208,16 +218,6 @@
 			else
 				user.visible_message("\blue [user] removes \the [tool] from [target]'s [affected.name].", \
 				"\blue There's something inside [target]'s [affected.name], but you just missed it this time." )
-		else if (affected.hidden)
-			user.visible_message("\blue [user] takes something out of incision on [target]'s [affected.name] with \the [tool].", \
-			"\blue You take something out of incision on [target]'s [affected.name]s with \the [tool]." )
-			affected.hidden.loc = get_turf(target)
-			if(!affected.hidden.blood_DNA)
-				affected.hidden.blood_DNA = list()
-			affected.hidden.blood_DNA[target.dna.unique_enzymes] = target.dna.b_type
-			affected.hidden.update_icon()
-			affected.hidden = null
-
 		else
 			user.visible_message("\blue [user] could not find anything inside [target]'s [affected.name], and pulls \the [tool] out.", \
 			"\blue You could not find anything inside [target]'s [affected.name]." )