diff --git a/src/org/ntlab/deltaViewer/CollaborationLayout.java b/src/org/ntlab/deltaViewer/CollaborationLayout.java
index bf3aad3..76674f9 100644
--- a/src/org/ntlab/deltaViewer/CollaborationLayout.java
+++ b/src/org/ntlab/deltaViewer/CollaborationLayout.java
@@ -83,7 +83,7 @@
 		}
 		
 		// Extract the reference access history.
-		List<Reference> references = objectCallGraph.getReferences();
+		List<Reference> references = new ArrayList<>(objectCallGraph.getReferences());
 		Map<Reference, List<Integer>> referenceHistory = new HashMap<>();
 		int order = 0;
 		for (Alias a: aliasCollector.getAliasList()) {
@@ -106,13 +106,28 @@
 			} else if (a.getAliasType() == AliasType.RETURN_VALUE) {
 				MethodExecution methodExec = a.getMethodExecution();
 				if (methodExec.getSignature().contains("List.get(") ||
-						methodExec.getSignature().contains("Map.get(")) {
+						methodExec.getSignature().contains("Map.get(") ||
+						methodExec.getSignature().contains(".next()") ||
+						methodExec.getSignature().contains(".iterator()") ||
+						methodExec.getSignature().contains(".listIterator()")) {
 					String srcObjId = methodExec.getThisObjId();
 					String dstObjId = methodExec.getReturnValue().getId();
 					String srcClassName = methodExec.getThisClassName();
 					String dstClassName = methodExec.getReturnValue().getActualType();
 					idx = references.indexOf(new Reference(srcObjId, dstObjId, srcClassName, dstClassName));
-				}				
+				} else if (methodExec.isStatic() && methodExec.getCallerMethodExecution().isStatic()) {
+					// For calls from a static method to another static method.
+					String dstClassName = methodExec.getThisClassName();
+					String srcClassName = methodExec.getCallerMethodExecution().getThisClassName();
+					String dstObjId = methodExec.getThisObjId() + ":" + dstClassName;
+					String srcObjId = methodExec.getCallerMethodExecution().getThisObjId() + ":" + srcClassName;
+					Reference r = new Reference(srcObjId, dstObjId, srcClassName, dstClassName);
+					idx = references.indexOf(r);
+					if (idx < 0) {
+						references.add(r);
+						idx = references.indexOf(r);
+					}					
+				}
 			} else if (a.getAliasType() == AliasType.CONSTRACTOR_INVOCATION) {
 				MethodInvocation c = (MethodInvocation) a.getOccurrencePoint().getStatement();
 				String srcObjId = a.getMethodExecution().getThisObjId();