These are really great links to explain blockage:
http://www.rabbit.org/journal/3-7/gi.html
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/171342.htm
“the cause of this condition is not the presence of hair in the stomach, but rather a GIT motility disorder that results in firm impacted stomach and cecal contents. If we do not correct the underlying problem, then this condition is destined to reoccur.”
“How do rabbits act when they have impacted stomach or cecal contents? They will stop eating either suddenly or gradually over a period of time. The stools will get smaller and smaller, then stop altogether. Often, these patients will be bright and alert for a week or longer. They may want to chew the paper on the bottom of the cage, the woodwork or the wall board (all sources of fiber they are craving), but refuse to eat their pellets. Some rabbits have had periodic soft, pudding-like stools prior to complete anorexia. Eventually these patients can become seriously ill and die if the condition is not treated.”
“Prevention is the best option. Providing a high fiber diet, avoiding stress and obesity, environmental enrichment, and daily combing to remove loose hair effectively prevents this condition. Clinical research does not support routine doses of mineral oil, wetting agents, or proteolytic enzymes as effective preventives.”
Read the links, they are great info.