diff --git a/systems.tex b/systems.tex
index 6eed4b592ae613f09d237ececce7256e7f2d83a1..0180a09db526fa32f50f749ad7823f7e5522abac 100644
--- a/systems.tex
+++ b/systems.tex
@@ -87,6 +87,8 @@ Opening such a letter and resealing it properly requires an \roll{Intelligence}{
 \subsection{Survival}
 
 \paragraph{Black-Walking} -- \roll{Dexterity}{Caving}, \tn[8].
+\index{Black Walking}
+\index{Spelunking!Black Walking}
 Despite every caver insisting on a good supply of torches and candles, they all end up feeling the ground in the dark eventually.
 Those who know their environment have a knack for crawling efficiently, feeling the surroundings through their fingertips and beards, and remembering every passage they took in the light simply through the sounds of their own breathing echoing uniquely in every cavern-segment.
 
@@ -100,6 +102,21 @@ A tie indicates that the shelter holds for a few hours, then collapses.
 Each Margin cures 1 \glspl{fatigue} caused by poison by the end of the interval.
 Of course if the roll fails, each failure margin \emph{inflicts} a \gls{fatigue}.
 
+\paragraph{Hypoxia} -- \roll{Intelligence}{Caving}, \tn[10].
+\label{hypoxia}
+\index{Hypoxia}
+\index{Spelunking!Hypoxia}
+Long, underground tunnels don't have a lot of oxygen.
+Taking a torch down one, or even staying down too long, and sucking up all the oxygen, can cause hypoxia.
+
+Once hypoxia begins, people will feel light headed, confused, and dizzy.
+
+If any \gls{pc} succeeds in the roll, they understand that hypoxia has settled in, and can put out their torches in order to stop the penalty increasing too quickly, and will probably try to move elsewhere.
+
+If the \glspl{pc} fail the roll, the \gls{gm} should increase the \gls{tn} for all rolls, without explaining why the \gls{tn} for various actions is so high, and continue increasing the \gls{tn} until the party find themselves weak, and confused, or manage to get out the other side.
+
+Once out, all penalties vanish, except for a single \gls{fatigue}.
+
 \subsection{Town Activities}
 
 \paragraph{Judging services} -- \roll{Wits}{Empathy}, \tn[9].
@@ -177,6 +194,7 @@ Success inflicts 2 \glspl{fatigue} on the person keeping watch.
 \paragraph{Climbing} -- \roll{Speed}{Athletics}.
 
 \paragraph{Detect sloping passages} -- \roll{Wits}{Caving}.
+\index{Spelunking!Detecting sloping passages}
 Understanding what altitude one has reached immediately indicates whether there might be running water, what type of rocks and minerals compose the surroundings (and therefore the chance of a cave-in), and how far one has to go to the surface.
 
 Despite gradual gradients, or sharp ups and downs, a good caver knows exactly how far they sit from the surface at all times.
@@ -225,6 +243,7 @@ Each failure margin adds 2 Miles to the journey time, so when trying to find a p
 If the roll is an 8, the actual journey would be 18 miles.
 
 \paragraph{Running in the Dark} -- \roll{Wits}{Caving}, \tn[12].
+\index{Spelunking!Running in the dark}
 A torch adds a +3 Bonus.
 A tie means the character comes to a sudden halt, without Damage.
 Failure means $1D6$ Damage, plus the character's Speed (running faster means more Damage).
diff --git a/traits.tex b/traits.tex
index e7a4a0c9d6055ba27edf67d2b86f768236af5061..df1c851c61ff470fc3322fed6ee22814774a7a7a 100644
--- a/traits.tex
+++ b/traits.tex
@@ -304,11 +304,11 @@ This covers all manner of fancy movements, from somersaults and rolling to climb
 \end{exampletext}
 
 \subsection{Caving}
+\index{Spelunking!Caving Skill}
 
 Caving includes navigation, foraging, building basic structures, and some understanding of the typical plants and beast found within caves.
 Just as most humans understand some basic Wyldcrafting, almost all dwarves and gnomes know a little of the Caving Skill.
 
-
 \begin{description}
   \item[\roll{Strength}{Caving}]
     covers throwing stone out of the way to form a path.
@@ -355,6 +355,7 @@ Just as most humans understand some basic Wyldcrafting, almost all dwarves and g
   They all laughed.
   Apparently hypoxia was some kind of joke to these idiots.
   The dwarf just sighed.
+  \index{Hypoxia}
   
 \end{exampletext}