diff --git a/luprex/core/cpp/spookyv2.cpp b/luprex/core/cpp/spookyv2.cpp
index e4628fd2..f8f368b7 100644
--- a/luprex/core/cpp/spookyv2.cpp
+++ b/luprex/core/cpp/spookyv2.cpp
@@ -298,6 +298,11 @@ void SpookyHash::Hash128(
     uint64_t *hash1, 
     uint64_t *hash2)
 {
+    if ((*hash1 == 0) && (*hash2 == 0)) {
+        *hash1 = 0x9438478934792837;
+        *hash2 = 0x8347848738748378;
+    }
+    
     if (length < sc_bufSize)
     {
         Short(message, length, hash1, hash2);
diff --git a/luprex/core/cpp/spookyv2.hpp b/luprex/core/cpp/spookyv2.hpp
index d1ce55b5..813fba1b 100644
--- a/luprex/core/cpp/spookyv2.hpp
+++ b/luprex/core/cpp/spookyv2.hpp
@@ -26,6 +26,9 @@
 // slower than MD5.
 //
 
+#ifndef SPOOKYV2_HPP
+#define SPOOKYV2_HPP
+
 #include <stddef.h>
 #include <cstdint>
 #include <utility>
@@ -43,5 +46,4 @@ public:
         uint64_t *hash2);     // input seed1, output hash1
 };
 
-
-
+#endif // SPOOKYV2_HPP
diff --git a/luprex/core/cpp/util.cpp b/luprex/core/cpp/util.cpp
index c8514448..0ddec568 100644
--- a/luprex/core/cpp/util.cpp
+++ b/luprex/core/cpp/util.cpp
@@ -28,7 +28,6 @@ std::string id_vector_debug_string(const IdVector &idv) {
     return oss.str();
 }
 
-
 IdVector sort_union_id_vectors(const IdVector &v1, const IdVector &v2) {
     IdVector result(v1.size() + v2.size());
     int next = 0;
@@ -47,6 +46,13 @@ IdVector sort_union_id_vectors(const IdVector &v1, const IdVector &v2) {
     return result;
 }
 
+HashValue hash_id_vector(const IdVector &idv) {
+    uint64_t hash1 = 0;
+    uint64_t hash2 = 0;
+    SpookyHash::Hash128(&idv[0], idv.size() * sizeof(int64_t), &hash1, &hash2);
+    return std::make_pair(hash1, hash2);
+}
+
 StringVec split(const std::string &s, char sep) {
     StringVec result;
     int start = 0;
diff --git a/luprex/core/cpp/util.hpp b/luprex/core/cpp/util.hpp
index e18dbca3..6ecd04dc 100644
--- a/luprex/core/cpp/util.hpp
+++ b/luprex/core/cpp/util.hpp
@@ -9,6 +9,7 @@
 #include <tuple>
 #include <utility>
 #include "luastack.hpp"
+#include "spookyv2.hpp"
 
 namespace util {
 
@@ -29,6 +30,9 @@ std::string id_vector_debug_string(const IdVector &idv);
 // Unions and sorts two ID vectors.
 IdVector sort_union_id_vectors(const IdVector &v1, const IdVector &v2);
 
+// Get a 64-bit hashvalue for an ID vector.
+HashValue hash_id_vector(const IdVector &idv);
+
 // Split a string into multiple strings
 StringVec split(const std::string &s, char sep);
 
diff --git a/luprex/core/cpp/world.cpp b/luprex/core/cpp/world.cpp
index 4b716b02..0117ae2f 100644
--- a/luprex/core/cpp/world.cpp
+++ b/luprex/core/cpp/world.cpp
@@ -185,7 +185,7 @@ std::string World::tangible_ids_debug_string() const {
 }
     
 
-util::IdVector World::get_near(int64_t player_id, float radius, bool exclude_nowhere) const {
+util::IdVector World::get_near_unsorted(int64_t player_id, float radius, bool exclude_nowhere) const {
     const Tangible *player = tangible_get(player_id);
     if (player == nullptr) {
         return IdVector();
@@ -200,6 +200,12 @@ util::IdVector World::get_near(int64_t player_id, float radius, bool exclude_now
     return plane_map_.scan_radius(aqback.plane(), aqback.xyz().x, aqback.xyz().y, radius, player_id);
 }
 
+util::IdVector World::get_near(int64_t player_id, float radius, bool exclude_nowhere) const {
+    util::IdVector v = get_near_unsorted(player_id, radius, exclude_nowhere);
+    std::sort(v.begin(), v.end());
+    return v;
+}
+
 Tangible *World::tangible_make(lua_State *L, int64_t id, bool pushdb) {
     // Get a state if we don't already have one.
     if (L == nullptr) {
@@ -550,8 +556,8 @@ void World::difference_transmit(int64_t actor_id, const World *master, StreamBuf
     // Get the list of tangibles visible in either model.
     // Some tangibles may be missing in the master, some may be missing in the sync.
     util::IdVector visible = util::sort_union_id_vectors(
-            master->get_near(actor_id, 100.0, true),
-            this->get_near(actor_id, 100.0, true));
+            master->get_near_unsorted(actor_id, RadiusVisibility, true),
+            get_near_unsorted(actor_id, RadiusVisibility, true));
     TanVector m_visible = master->tangible_get_all(visible);
     TanVector s_visible = tangible_get_all(visible);
     assert(m_visible.size() == s_visible.size());
@@ -575,12 +581,24 @@ void World::difference_transmit(int64_t actor_id, const World *master, StreamBuf
         }
     }
 
+    // Obtain the list of tangibles whose tables we're going to transmit.
+    util::IdVector closetans = get_near(actor_id, RadiusClose, true);
+    assert(closetans == master->get_near(actor_id, RadiusClose, true));
+    util::HashValue closehash = util::hash_id_vector(closetans);
+
+    // Confirm the close tangibles with the client.
+    sb->write_hashvalue(closehash);
+
     assert(tsb.at_eof());
 }
 
 void World::apply_differences(StreamBuffer *sb) {
-    patch_actor_essentials(sb);
+    int64_t actor_id = patch_actor_essentials(sb);
     patch_visible_animations(sb);
+    util::IdVector closetans = get_near(actor_id, RadiusClose, true);
+    util::HashValue closehash = util::hash_id_vector(closetans);
+    util::HashValue m_closehash = sb->read_hashvalue();
+    assert(closehash == m_closehash);
 }
 
 void World::diff_actor_essentials(const Tangible *m_actor, const Tangible *s_actor, StreamBuffer *sb) {
@@ -594,7 +612,7 @@ void World::diff_actor_essentials(const Tangible *m_actor, const Tangible *s_act
     }
 }
 
-void World::patch_actor_essentials(StreamBuffer *sb) {
+int64_t World::patch_actor_essentials(StreamBuffer *sb) {
     int64_t actor_id = sb->read_int64();
     Tangible *s_actor = tangible_get(actor_id);
     if (s_actor == nullptr) {
@@ -606,6 +624,7 @@ void World::patch_actor_essentials(StreamBuffer *sb) {
         s_actor->anim_queue_.patch(sb);
     }
     s_actor->update_plane_item();
+    return actor_id;
 }
 
 void World::diff_visible_animations(const TanVector &mvis, const TanVector &svis, StreamBuffer *sb) {
diff --git a/luprex/core/cpp/world.hpp b/luprex/core/cpp/world.hpp
index 950a2d22..48825004 100644
--- a/luprex/core/cpp/world.hpp
+++ b/luprex/core/cpp/world.hpp
@@ -80,6 +80,8 @@ public:
     using IdVector = util::IdVector;
     using TanVector = std::vector<const Tangible*>;
     using Redirects = std::map<int64_t, int64_t>;
+    const float RadiusVisibility = 100.0;
+    const float RadiusClose = 10.0; 
 
     // Constructor.
     //
@@ -103,9 +105,11 @@ public:
     // get_near
     //
     // Get a list of the tangibles that are near the player.  If 'exclude_nowhere' is
-    // true, exclude any tangibles on the nowhere plane.
+    // true, exclude any tangibles on the nowhere plane.  The unsorted version returns
+    // the tangibles in an unpredictable order.
     //
     IdVector get_near(int64_t player_id, float radius, bool exclude_nowhere) const;
+    IdVector get_near_unsorted(int64_t player_id, float radius, bool exclude_nowhere) const;
     
     // Make a tangible.
     //
@@ -247,7 +251,7 @@ private:
     // We also update the actor's ID allocation pipeline.
     //
     static void diff_actor_essentials(const Tangible *mactor, const Tangible *sactor, StreamBuffer *sb); 
-    void patch_actor_essentials(StreamBuffer *sb);
+    int64_t patch_actor_essentials(StreamBuffer *sb);
 
     // Pass 2 of difference transmission: visible animations.
     //