diff --git a/public/js/app.js b/public/js/app.js
index 9010595..e02064e 100644
--- a/public/js/app.js
+++ b/public/js/app.js
@@ -982,6 +982,10 @@
           const isSeattleJapan = ( (lowS === 'seattle' || lowS === 'us seattle') && lowD === 'japan' ) ||
                                  ( (lowD === 'seattle' || lowD === 'us seattle') && lowS === 'japan' );
 
+          // Canonical hash for deterministic randomization (period, etc)
+          const names = [lowS, lowD].sort();
+          const routeHash = names.join('').split('').reduce((acc, c) => acc + c.charCodeAt(0), 0);
+
           let finalCurve = 0;
           if (isSeattleJapan) {
             // Special rule: Seattle ↔ Japan route curves upward (North)
@@ -1006,7 +1010,7 @@
             latencyLine: true,
             effect: {
               show: true,
-              period: 4,
+              period: 3 + ((routeHash + i) % 5), // Deterministic random period: 3-7s to vary start/speed
               trailLength: 0.1,
               color: 'rgba(99, 102, 241, 0.8)',
               symbol: 'arrow',