Proc to define

code/modules/mob/living/carbon/inventory.dm

@@ -140,9 +140,3 @@
 /mob/living/carbon/proc/get_holding_bodypart_of_item(obj/item/I)
 	var/index = get_held_index_of_item(I)
 	return index && hand_bodyparts[index]
-
-/mob/living/carbon/proc/get_internal_slots()
-	return list(
-		head,
-		wear_mask,
-		)

code/modules/mob/living/carbon/life.dm

@@ -306,12 +306,8 @@
 /mob/living/carbon/proc/get_breath_from_internal(volume_needed)
 	var/obj/item/clothing/check
 	var/internals = FALSE
-	var/internalslots = list(
-		head,
-		wear_mask,
-		)
 
-	for(check in internalslots)
+	for(check in GET_INTERNAL_SLOTS(src))
 		if(CHECK_BITFIELD(check.clothing_flags, ALLOWINTERNALS))
 			internals = TRUE
 	if(internal)