diff --git a/life/src/main.rs b/life/src/main.rs
index c304b25..02d3617 100644
--- a/life/src/main.rs
+++ b/life/src/main.rs
@@ -1,15 +1,14 @@
 // TODO:
 //  * Volume slider
-//  * Invert mute/unmute icons
 //  * Only move camera when cells move out of view
+//      * "Follow" enhancement: Zoom in/out
+//  * optimize simulation_step
 //  * Stop creating cells when I didn't mean to (clicking UI, click + dragging)
 //  * Keep some controls open when main ui panel is closed
-//  * Exclude power button from web build
 //  * Show shadow of piece (same tile, just with alpha transparency)
 //  * Dark mode
 //  * Make click and drag feel better
 //      * Add arrow keys to move around
-//  * "Follow" enhancement: Zoom in/out
 #![allow(clippy::complexity)]
 // Only because of FromTemplat macros unfortunately...
 #![allow(dead_code)]
@@ -821,61 +820,45 @@ enum SimulationPlayback {
 fn simulation_step(
     q: Query<(Entity, &Coordinates), With<Cell>>,
     mut writer: MessageWriter<Lifecycle>,
+    mut alive: Local<HashMap<Coordinates, Entity>>,
+    mut candidates: Local<HashSet<Coordinates>>,
 ) {
-    fn is_cell_alive(
-        coordinates: &Coordinates,
-        query: &Query<(Entity, &Coordinates), With<Cell>>,
-    ) -> bool {
-        query.iter().any(|(_e, c)| *c == *coordinates)
-    }
-
-    fn living_neighbors(
-        c: &Coordinates,
-        query: &Query<(Entity, &Coordinates), With<Cell>>,
-    ) -> usize {
+    let living_neighbors = |a: &HashMap<Coordinates, Entity>, c: &Coordinates| -> usize {
         c.neighbors()
             .filter(|neighbor| {
-                query
-                    .iter()
-                    .any(|(_e, coordinates)| *neighbor == *coordinates)
+                a.contains_key(neighbor)
             })
             .count()
-    }
+    };
 
-    fn cell_entity(
-        coordinates: &Coordinates,
-        query: Query<(Entity, &Coordinates), With<Cell>>,
-    ) -> Option<Entity> {
-        query
-            .iter()
-            .find_map(|(e, c)| (*c == *coordinates).then_some(e))
-    }
+    // Reset alive cell cache
+    *alive = q.iter().map(|(e, c)| (c.clone(), e)).collect();
 
-    // Collect list of candidate positions...
-    let mut coordinates: HashSet<Coordinates> = HashSet::new();
+    // Clear candidate coordinates
+    candidates.clear();
 
     // Put all dead cells neighboring living cells into the coordinates hashset
     // Each living cell
     q.iter().for_each(|(_e, c)| {
-        coordinates.insert(c.clone());
+        candidates.insert(c.clone());
         // Iterator over neighbor positions
         // Filter to just dead neighbors
         c.neighbors()
-            .filter(|c| !is_cell_alive(c, &q))
+            .filter(|c| !alive.contains_key(c))
             .for_each(|c| {
-                coordinates.insert(c);
+                candidates.insert(c);
             });
     });
 
     // Get Neighbor Count of living cells
-    coordinates.iter().for_each(|c| {
-        let num_living_neighbors = living_neighbors(c, &q);
-        let is_living = is_cell_alive(c, &q);
+    candidates.iter().for_each(|c| {
+        let num_living_neighbors = living_neighbors(&*alive, c);
+        let is_living = alive.contains_key(c);
 
         match num_living_neighbors {
             ..2 | 4.. => {
                 if is_living {
-                    writer.write(Lifecycle::Dead(cell_entity(c, q).unwrap()));
+                    writer.write(Lifecycle::Dead(alive.get(c).cloned().unwrap()));
                 }
             }
             2 => debug!("continue"),