diff --git a/HISTORY.md b/HISTORY.md
index a1e672d7..a7a57237 100755
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,6 +2,9 @@
 
 ## in development
 
+###2018-12-28
+* Blocks, Threads: added 'neg' selector to monad operator dropdown
+
 ### 2018-12-07
 * GUI: fixed #2284 (executing "inherit" should not un-hide palette in presentation mode)
 
diff --git a/snap.html b/snap.html
index f24b9b1e..96f6e876 100755
--- a/snap.html
+++ b/snap.html
@@ -6,8 +6,8 @@
         <link rel="shortcut icon" href="src/favicon.ico">
         <script type="text/javascript" src="src/morphic.js?version=2018-10-02"></script>
         <script type="text/javascript" src="src/widgets.js?version=2018-10-02"></script>
-        <script type="text/javascript" src="src/blocks.js?version=2018-11-13"></script>
-        <script type="text/javascript" src="src/threads.js?version=2018-10-26"></script>
+        <script type="text/javascript" src="src/blocks.js?version=2018-12-28"></script>
+        <script type="text/javascript" src="src/threads.js?version=2018-12-28"></script>
         <script type="text/javascript" src="src/objects.js?version=2018-11-28"></script>
         <script type="text/javascript" src="src/gui.js?version=2018-12-07"></script>
         <script type="text/javascript" src="src/paint.js?version=2018-10-02"></script>
diff --git a/src/blocks.js b/src/blocks.js
index 4bb02bd6..113f870c 100644
--- a/src/blocks.js
+++ b/src/blocks.js
@@ -148,7 +148,7 @@ CustomCommandBlockMorph, SymbolMorph, ToggleButtonMorph, DialMorph*/
 
 // Global stuff ////////////////////////////////////////////////////////
 
-modules.blocks = '2018-November-13';
+modules.blocks = '2018-December-28';
 
 var SyntaxElementMorph;
 var BlockMorph;
@@ -1257,6 +1257,7 @@ SyntaxElementMorph.prototype.labelPart = function (spec) {
                 false,
                 {
                     abs : ['abs'],
+                    neg : ['neg'],
                     ceiling : ['ceiling'],
                     floor : ['floor'],
                     sqrt : ['sqrt'],
diff --git a/src/threads.js b/src/threads.js
index 779d6d73..5f8bd516 100644
--- a/src/threads.js
+++ b/src/threads.js
@@ -62,7 +62,7 @@ StageMorph, SpriteMorph, StagePrompterMorph, Note, modules, isString, copy,
 isNil, WatcherMorph, List, ListWatcherMorph, alert, console, TableMorph,
 TableFrameMorph, ColorSlotMorph, isSnapObject, Map*/
 
-modules.threads = '2018-October-26';
+modules.threads = '2018-December-28';
 
 var ThreadManager;
 var Process;
@@ -2609,6 +2609,9 @@ Process.prototype.reportMonadic = function (fname, n) {
     case 'abs':
         result = Math.abs(x);
         break;
+    case 'neg':
+        result = n * -1;
+        break;
     case 'ceiling':
         result = Math.ceil(x);
         break;
@@ -3158,6 +3161,13 @@ Process.prototype.objectTouchingObject = function (thisObj, name) {
             }
             if (those.some(function (any) {
                     return any.isVisible && thisObj.isTouching(any);
+                    // check collision with any part, performance issue
+                    // commented out for now
+                /*
+                    return any.allParts().some(function (part) {
+                        return part.isVisible && thisObj.isTouching(part);
+                    })
+                */
                 })) {
                 return true;
             }