+-------+ +----------+         +----+           
| dogs  | |replica 1 |         | a  |           
|       | |          |         |    |           
+-------+ +----------+         +----+           
    |           ^                |              
    |           |                |              
    |           v                |              
    |     +----------+           |              
    |     |replica 2 |           |              
  chase   |       To err is human, to moo bovine
    |     +----------+           |              
    |                            |              
    |                            |  *           
    v                            v              
+-------+                      +----+           
| cats  |                      | b  |           
|       |                      |    |           
+-------+                      +----+           
    |                                           
  chase                                         
    |                                           
    v                                           
+-------+                                       
| mice  |                                       
|       |                                       
+-------+                                       
