Removes magic numbers and an useless check

- it shouldn’t runtime.

code/game/objects/effects/effect_system.dm

@@ -846,7 +846,7 @@ steam.start() -- spawns the effect
 
 	if (istype(AM, /mob/living/carbon))
 		var/mob/living/carbon/M = AM
-		M.slip(5, 2, src, 1)
+		M.slip(5, 2, src)
 
 
 /datum/effect/effect/system/foam_spread

code/game/objects/items/devices/PDA/PDA.dm

@@ -961,7 +961,7 @@ var/global/list/obj/item/device/pda/PDAs = list()
 /obj/item/device/pda/clown/Crossed(AM as mob|obj) //Clown PDA is slippery.
 	if (istype(AM, /mob/living/carbon))
 		var/mob/living/carbon/M = AM
-		if(M.slip(8, 5, src))
+		if(M.slip(8, 5, src, NO_SLIP_WHEN_WALKING))
 			if (ishuman(M) && (M.real_name != src.owner))
 				if (istype(src.cartridge, /obj/item/weapon/cartridge/clown))
 					var/obj/item/weapon/cartridge/clown/cart = src.cartridge

code/game/objects/items/weapons/clown_items.dm

@@ -11,7 +11,7 @@
 /obj/item/weapon/bananapeel/Crossed(AM as mob|obj)
 	if (istype(AM, /mob/living/carbon))
 		var/mob/living/carbon/M = AM
-		M.slip(4, 2, src, 1)
+		M.slip(4, 2, src)
 
 
 /*
@@ -20,7 +20,7 @@
 /obj/item/weapon/soap/Crossed(AM as mob|obj) //EXACTLY the same as bananapeel for now, so it makes sense to put it in the same dm -- Urist
 	if (istype(AM, /mob/living/carbon))
 		var/mob/living/carbon/M = AM
-		M.slip(3, 2, src, 1)
+		M.slip(3, 2, src)
 
 /obj/item/weapon/soap/afterattack(atom/target, mob/user as mob, proximity)
 	if(!proximity) return

code/game/turfs/simulated.dm

@@ -55,12 +55,12 @@
 
 		switch (src.wet)
 			if(1) //wet floor
-				if(!M.slip(8, 5, null, 2))
+				if(!M.slip(8, 5, null, (NO_SLIP_WHEN_WALKING|STEP)))
 					M.inertia_dir = 0
 				return
 
 			if(2) //lube
-				M.slip(0, 10, null, 3)
+				M.slip(0, 10, null, (STEP|SLIDE|GALOSHES_DONT_HELP))
 
 
 	..()

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

@@ -548,24 +548,21 @@
 		return "trails_1"
 	return "trails_2"
 
-/*
- * 0)clown pda == no slip when walking, lube=0
- * 1)banana peels, soap and foam == slip when walking, lube=1
- * 2)Wet floor == no slip when walking, take a step, lube=2
- * 3)Lube == always slips, sliding effect, lube=3
- */
+var/const/NO_SLIP_WHEN_WALKING = 1
+var/const/STEP = 2
+var/const/SLIDE = 4
+var/const/GALOSHES_DONT_HELP = 8
 /mob/living/carbon/slip(var/s_amount, var/w_amount, var/obj/O, var/lube)
-	if (m_intent=="walk" && (lube==0 || lube==2))
+	if (m_intent=="walk" && (lube&NO_SLIP_WHEN_WALKING))
 		return 0
 	if(!lying)
 		stop_pulling()
-		if(lube==2 || lube==3)
+		if(lube&STEP)
 			step(src, src.dir)
-		if(lube==3)
+		if(lube&SLIDE)
 			for(var/i=1, i<5, i++)
 				spawn (i)
-					if(src)
-						step(src, src.dir)
+					step(src, src.dir)
 			take_organ_damage(2)
 		if(O)
 			src << "<span class='notice'>You slipped on the [O.name]!</span>"

code/modules/mob/living/carbon/human/human_movement.dm

@@ -67,6 +67,6 @@
 
 
 /mob/living/carbon/human/slip(var/s_amount, var/w_amount, var/obj/O, var/lube)
-	if(isobj(src.shoes) && src.shoes.flags&NOSLIP && lube!=3)
+	if(isobj(shoes) && (shoes.flags&NOSLIP) && !(lube&GALOSHES_DONT_HELP))
 		return 0
 	.=..()