diff --git a/panda/src/collide/collisionHandlerEvent.I b/panda/src/collide/collisionHandlerEvent.I
index 045ad796e6..735c7a1d41 100644
--- a/panda/src/collide/collisionHandlerEvent.I
+++ b/panda/src/collide/collisionHandlerEvent.I
@@ -50,6 +50,14 @@ operator = (const CollisionHandlerEvent::SortEntries &) {
 //               The event name will be based on the in_pattern
 //               string specified here, with all occurrences of the
 //               above strings replaced with the corresponding values.
+//
+//               In general, the in_pattern event is thrown on the
+//               first detection of a collision between two particular
+//               nodes.  In subsequent passes, as long as a collision
+//               between those two nodes continues to be detected each
+//               frame, the again_pattern is thrown.  The first frame
+//               in which the collision is no longer detected, the
+//               out_pattern event is thrown.
 ////////////////////////////////////////////////////////////////////
 INLINE void CollisionHandlerEvent::
 set_in_pattern(const string &in_pattern) {
@@ -68,6 +76,42 @@ get_in_pattern() const {
   return _in_pattern;
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionHandlerEvent::set_again_pattern
+//       Access: Public
+//  Description: Sets the pattern string that indicates how the event
+//               names are generated when a collision between two
+//               particular nodes is *still* detected.  This event is
+//               each consecutive time a collision between two
+//               particular nodes is detected, starting with the
+//               second time.
+//
+//               In general, the in_pattern event is thrown on the
+//               first detection of a collision between two particular
+//               nodes.  In subsequent passes, as long as a collision
+//               between those two nodes continues to be detected each
+//               frame, the again_pattern is thrown.  The first frame
+//               in which the collision is no longer detected, the
+//               out_pattern event is thrown.
+////////////////////////////////////////////////////////////////////
+INLINE void CollisionHandlerEvent::
+set_again_pattern(const string &again_pattern) {
+  _again_pattern = again_pattern;
+}
+
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionHandlerEvent::get_again_pattern
+//       Access: Public
+//  Description: Returns the pattern string that indicates how the
+//               event names are generated when a collision between
+//               two particular nodes is *still* detected.  See
+//               set_again_pattern() and set_in_pattern().
+////////////////////////////////////////////////////////////////////
+INLINE string CollisionHandlerEvent::
+get_again_pattern() const {
+  return _again_pattern;
+}
+
 
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionHandlerEvent::set_out_pattern
@@ -78,12 +122,11 @@ get_in_pattern() const {
 //
 //               In general, the in_pattern event is thrown on the
 //               first detection of a collision between two particular
-//               nodes.  Thereafter, as long as a collision between
-//               those two nodes continues to be detected each frame,
-//               no further events (associated with this particular
-//               pair of nodes) are thrown.  The first frame in which
-//               the collision is no longer detected, the out_pattern
-//               event is thrown.
+//               nodes.  In subsequent passes, as long as a collision
+//               between those two nodes continues to be detected each
+//               frame, the again_pattern is thrown.  The first frame
+//               in which the collision is no longer detected, the
+//               out_pattern event is thrown.
 ////////////////////////////////////////////////////////////////////
 INLINE void CollisionHandlerEvent::
 set_out_pattern(const string &out_pattern) {
diff --git a/panda/src/collide/collisionHandlerEvent.cxx b/panda/src/collide/collisionHandlerEvent.cxx
index 84a6b41165..69d13ac161 100644
--- a/panda/src/collide/collisionHandlerEvent.cxx
+++ b/panda/src/collide/collisionHandlerEvent.cxx
@@ -105,6 +105,7 @@ end_group() {
 
     } else {
       // This element is in both b and a.  It hasn't changed.
+      throw_event_pattern(_again_pattern, *cb);
       ++ca;
       ++cb;
     }
@@ -125,6 +126,27 @@ end_group() {
   }
 }
 
+////////////////////////////////////////////////////////////////////
+//     Function: CollisionHandlerEvent::clear
+//       Access: Public
+//  Description: Empties the list of elements that all colliders are
+//               known to be colliding with.  No "out" events will be
+//               thrown; if the same collision is detected next frame,
+//               a new "in" event will be thrown for each collision.
+//
+//               This can be called each frame to defeat the
+//               persistant "in" event mechanism, which prevents the
+//               same "in" event from being thrown repeatedly.
+//               However, also see set_again_pattern(), which can be
+//               used to set the event that is thrown when a collision
+//               is detected for more than one consecutive frames.
+////////////////////////////////////////////////////////////////////
+void CollisionHandlerEvent::
+clear() {
+  _last_colliding.clear();
+  _current_colliding.clear();
+}
+
 ////////////////////////////////////////////////////////////////////
 //     Function: CollisionHandlerEvent::throw_event_pattern
 //       Access: Private
diff --git a/panda/src/collide/collisionHandlerEvent.h b/panda/src/collide/collisionHandlerEvent.h
index cf0a687dad..22c95d6a6c 100644
--- a/panda/src/collide/collisionHandlerEvent.h
+++ b/panda/src/collide/collisionHandlerEvent.h
@@ -35,13 +35,18 @@ public:
 PUBLISHED:
   INLINE void set_in_pattern(const string &pattern);
   INLINE string get_in_pattern() const;
+  INLINE void set_again_pattern(const string &pattern);
+  INLINE string get_again_pattern() const;
   INLINE void set_out_pattern(const string &pattern);
   INLINE string get_out_pattern() const;
 
+  void clear();
+
 private:
   void throw_event_pattern(const string &pattern, CollisionEntry *entry);
 
   string _in_pattern;
+  string _again_pattern;
   string _out_pattern;
 
   int _index;