So I decided to find out why Nuatilus delays to syntax highlight when I open ChronosManager I open my activity monitor to be amazed by the fact that pharo was consuming 30% of one of my cores. At the time I thought it was my fault because when my GUI steps I load from a png a form that I attack to a Morph. So I optomised that part loading all the pngs before hand , creating all the forms and during steping point only to the correct form. Nope still 30% ok change step time to 1 sec Nope still 30% ok delete step and step time alltogether Nope still 30% so the only explanation left is that pharo does not like I use images , which are not that big anyway , my whole image library is just 1 mb. So how I profile this ? Is there any way to find exactly where that 30% is consumed ? I tried to profile step and it retunred back with a mere 32ms , and I suspect thats the first step that loads the images , the second step would be much faster since it will just point to correct forms. So with a step of 32ms max and stepping once per second why a 30% CPU consumption ?