Fixing borer infestation logic.

code/modules/mob/living/human/human_defense.dm

@@ -85,20 +85,6 @@ meteor_act
 	// Add inherent armor to the end of list so that protective equipment is checked first
 	. += ..()
 
-/mob/living/human/proc/check_head_coverage()
-	for(var/slot in global.standard_headgear_slots)
-		var/obj/item/clothing/clothes = get_equipped_item(slot)
-		if(istype(clothes) && (clothes.body_parts_covered & SLOT_HEAD))
-			return TRUE
-	return FALSE
-
-//Used to check if they can be fed food/drinks/pills
-/mob/living/human/check_mouth_coverage()
-	for(var/slot in global.standard_headgear_slots)
-		var/obj/item/gear = get_equipped_item(slot)
-		if(istype(gear) && (gear.body_parts_covered & SLOT_FACE) && !(gear.item_flags & ITEM_FLAG_FLEXIBLEMATERIAL))
-			return gear
-
 /mob/living/human/resolve_item_attack(obj/item/I, mob/living/user, var/target_zone)
 
 	for (var/obj/item/grab/grab as anything in grabbed_by)

code/modules/mob/mob_eating.dm

@@ -1,6 +1,15 @@
-// mobs do not have blocked mouths by default
-// overridden in human_defense.dm
+//Used to check if they can be fed food/drinks/pills
 /mob/proc/check_mouth_coverage()
+	return get_covering_head_item(SLOT_FACE)
+
+/mob/proc/check_head_coverage()
+	return !!get_covering_head_item(SLOT_HEAD)
+
+/mob/proc/get_covering_head_item(slot_flags)
+	for(var/slot in global.standard_headgear_slots)
+		var/obj/item/clothes = get_equipped_item(slot)
+		if(istype(clothes) && (clothes.body_parts_covered & slot_flags) && !(clothes.item_flags & ITEM_FLAG_FLEXIBLEMATERIAL))
+			return clothes
 	return null
 
 /mob/proc/get_eaten_transfer_amount(var/default)

mods/mobs/borers/mob/borer/borer.dm

@@ -20,6 +20,22 @@
 	bleed_colour = "#816e12"
 	ai = /datum/mob_controller/borer
 
+	// Defined here to remove relaymove handlers as being
+	// directly in mob contents breaks relaymove spectacularly.
+	movement_handlers = list(
+		/datum/movement_handler/mob/death,
+		/datum/movement_handler/mob/borer_in_host,
+		/datum/movement_handler/mob/conscious,
+		/datum/movement_handler/mob/eye,
+		/datum/movement_handler/mob/delay,
+		/datum/movement_handler/mob/stop_effect,
+		/datum/movement_handler/mob/physically_capable,
+		/datum/movement_handler/mob/physically_restrained,
+		/datum/movement_handler/mob/space,
+		/datum/movement_handler/mob/multiz,
+		/datum/movement_handler/mob/movement
+	)
+
 	var/static/list/chemical_types = list(
 		"anti-trauma" =  /decl/material/liquid/brute_meds,
 		"amphetamines" = /decl/material/liquid/amphetamines,
@@ -42,6 +58,9 @@
 	var/mob/living/human/host        // Human host for the brain worm.
 	var/mob/living/captive_brain/host_brain // Used for swapping control of the body back and forth.
 
+/datum/movement_handler/mob/borer_in_host/MayMove(mob/mover, is_external)
+	return ismob(mob.loc) ? MOVEMENT_STOP : MOVEMENT_PROCEED
+
 /datum/mob_controller/borer
 	emote_hear = list("chirrups")
 	do_wander = FALSE

mods/mobs/borers/mob/borer/borer_attacks.dm

@@ -1,50 +1,44 @@
 /mob/living/simple_animal/borer/UnarmedAttack(atom/A, proximity)
 
-	. = ..()
-	if(.)
-		return
+	if(host)
+		return TRUE // We cannot click things outside of our host.
 
-	if(!isliving(A) || a_intent != I_GRAB)
-		return FALSE
+	if(!isliving(A) || a_intent != I_GRAB || stat || !proximity)
+		return ..()
 
-	if(host || !can_use_borer_ability(requires_host_value = FALSE, check_last_special = FALSE))
-		return FALSE
+	if(!can_use_borer_ability(requires_host_value = FALSE, check_last_special = FALSE))
+		return TRUE
 
-	var/mob/living/M = A
-	if(M.has_brain_worms())
+	var/mob/living/victim = A
+	if(victim.has_brain_worms())
 		to_chat(src, SPAN_WARNING("You cannot take a host who already has a passenger!"))
 		return TRUE
-
-	//TODO generalize borers to enter any mob. Until then, return early.
-	if(!ishuman(M))
-		to_chat(src, SPAN_WARNING("This creature is not sufficiently intelligent to host you."))
+	var/obj/item/organ/external/limb = GET_EXTERNAL_ORGAN(victim, BP_HEAD)
+	if(!limb)
+		to_chat(src, SPAN_WARNING("\The [victim] does not have anatomy compatible with your lifecycle!"))
 		return TRUE
-	// end TODO
-
-	var/mob/living/human/H = M
-	var/obj/item/organ/external/E = GET_EXTERNAL_ORGAN(H, BP_HEAD)
-	if(!E)
-		to_chat(src, SPAN_WARNING("\The [H] does not have a head!"))
+	if(BP_IS_PROSTHETIC(limb))
+		to_chat(src, SPAN_WARNING("\The [victim]'s head is prosthetic and cannot support your lifecycle!"))
 		return TRUE
-	if(!H.should_have_organ(BP_BRAIN))
-		to_chat(src, SPAN_WARNING("\The [H] does not seem to have a brain cavity to enter."))
+	if(!victim.should_have_organ(BP_BRAIN))
+		to_chat(src, SPAN_WARNING("\The [victim] does not seem to have a brain cavity to enter."))
 		return TRUE
-	if(H.check_head_coverage())
+	if(victim.check_head_coverage())
 		to_chat(src, SPAN_WARNING("You cannot get through that host's protective gear."))
 		return TRUE
 
-	to_chat(M, SPAN_WARNING("Something slimy begins probing at the opening of your ear canal..."))
-	to_chat(src, SPAN_NOTICE("You slither up [M] and begin probing at their ear canal..."))
+	to_chat(victim, SPAN_WARNING("Something slimy begins probing at the opening of your ear canal..."))
+	to_chat(src, SPAN_NOTICE("You slither up [victim] and begin probing at their ear canal..."))
 	set_ability_cooldown(5 SECONDS)
 
-	if(!do_after(src, 3 SECONDS, M))
+	if(!do_after(src, 3 SECONDS, victim) || host || GET_EXTERNAL_ORGAN(victim, BP_HEAD) != limb || BP_IS_PROSTHETIC(limb) || victim.check_head_coverage())
 		return TRUE
 
-	to_chat(src, SPAN_NOTICE("You wiggle into \the [M]'s ear."))
-	if(M.stat == CONSCIOUS)
-		to_chat(M, SPAN_DANGER("Something wet, cold and slimy wiggles into your ear!"))
+	to_chat(src, SPAN_NOTICE("You wiggle into \the [victim]'s ear."))
+	if(victim.stat == CONSCIOUS)
+		to_chat(victim, SPAN_DANGER("Something wet, cold and slimy wiggles into your ear!"))
 
-	host = M
+	host = victim
 	host.status_flags |= PASSEMOTES
 	forceMove(host)
 
@@ -60,9 +54,9 @@
 		borers.add_antagonist_mind(host.mind, 1, borers.faction_name, borers.faction_welcome)
 
 	if(ishuman(host))
-		var/obj/item/organ/internal/I = GET_INTERNAL_ORGAN(H, BP_BRAIN)
+		var/obj/item/organ/internal/I = GET_INTERNAL_ORGAN(victim, BP_BRAIN)
 		if(!I) // No brain organ, so the borer moves in and replaces it permanently.
 			replace_brain()
-		else if(E) // If they're in normally, implant removal can get them out.
-			LAZYDISTINCTADD(E.implants, src)
+		else if(limb) // If they're in normally, implant removal can get them out.
+			LAZYDISTINCTADD(limb.implants, src)
 	return TRUE

mods/mobs/borers/mob/borer/borer_hud.dm

@@ -50,6 +50,7 @@
 	icon = 'mods/mobs/borers/icons/borer_ui.dmi'
 	alpha = 0
 	invisibility = INVISIBILITY_MAXIMUM
+	requires_ui_style = FALSE
 
 /obj/screen/borer/handle_click(mob/user, params)
 	if(!isborer(user))