From an applicable generalized 1/4 Tag.
Very Centers and the directly facing Outside dancers do a Pass Thru as the End
  of the Center Line 
  Counter Rotate 1/4
  (on the Outside); Centers of each side Hinge; Center 4 Star 1/4 as Outsides Trade; Those who meet
  Cast Off 3/4 as Others move up (Phantom Hourglass Circulate).
Ends in Parallel Lines|Waves.
Notes:
- 
Those doing the Pass Thru should point at each other before
    moving.  The Outside dancer who is not doing the Pass
    Thru should not move until one of the original Very Centers has
    appeared by his/her side.  Should you prematurely turn in anticipation
    of the Hinge you will likely throw yourself (as well as other dancers)
    out of position.
- 
Be careful and dance each part of Chain Reaction very precisely
    since the Hinge could be from a Mini-Wave or from a Couple; the
    Outsides Trade could be from a Mini-Wave or a Couple; the Star could
    be normal or facing; and the final Cast Off 3/4 could be
    an Arm Turn or a 'Push' Cast.  Don't rush the execution of this call
    since teamwork is required for successful completion.
From symmetric starting formations, 
Chain Reaction (Star 1/4 or Star 3/4)
  always ends in Parallel Lines.  It never ends in a Parallelogram.  
  
Chain Reaction, Star 1/2 sometimes ends in a Parallelogram.
Listed below are the eight possible symmetric starting formations and
  corresponding ending formations for Chain Reaction.
|  | 
  | Starting formation | Ending formation | Ending formation |  
  | Centers | Outsides | (after Star 1/4  or  3/4) | (after Star 1/2) |  
  | R-H Wave | Couple | R-H Waves | R-H Waves |  
  | L-H Wave | Couple | L-H Waves | L-H Waves |  
  | R-H Wave | R-H Mini-Wave | L-H 2FL | Parallelogram 3 & 1 Lines |  
  | L-H Wave | L-H Mini-Wave | L-H Waves | L-H Waves |  
  | R-H 2FL | Couple | 3 & 1 Lines | 3 & 1 Lines |  
  | L-H 2FL | Couple | 3 & 1 Lines | 3 & 1 Lines |  
  | R-H 2FL | L-H Mini-Wave | 3 & 1 Lines | 3 & 1 Lines |  
  | L-H 2FL | R-H Mini-Wave | 3 & 1 Lines | Parallelogram R-H Waves |  |