diff --git a/src/world.rs b/src/world.rs
index ab5cdde..763c90a 100644
--- a/src/world.rs
+++ b/src/world.rs
@@ -3,7 +3,7 @@ use crate::value::Value;
 use crate::vm::{Creature, Panic};
 use ran::ran_u8;
 use std::cell::RefCell;
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::mem::swap;
 use std::rc::Rc;
 use std::time::{Duration, Instant};
@@ -67,7 +67,7 @@ pub struct Zoo {
     procs: Vec<Status>,
     empty: Vec<usize>,
     ids: HashMap<&'static str, usize>,
-    dead: Vec<&'static str>,
+    dead: HashSet<&'static str>,
     kill_list: Vec<&'static str>,
     sleeping: HashMap<&'static str, (Instant, Duration)>,
     active_idx: usize,
@@ -81,7 +81,7 @@ impl Zoo {
             empty: vec![],
             ids: HashMap::new(),
             kill_list: vec![],
-            dead: vec![],
+            dead: HashSet::new(),
             sleeping: HashMap::new(),
             active_idx: 0,
             active_id: "",
@@ -155,7 +155,7 @@ impl Zoo {
                 self.procs[*idx] = Status::Empty;
                 self.empty.push(*idx);
                 self.ids.remove(id);
-                self.dead.push(id);
+                self.dead.insert(id);
             }
         }