I would say it is in the shape of the parent being kept out of their lives.  We have to acknowledge that alienation happens to both moms and dads.  Frankly anyone who would do this a child, is a disgusting human being.  I am not sure how anyone can be immune to the obvious signs of a child whose soul is being crushed by the hate one parent has for the other.

Another great website with some super practical tips for dealing with the alienation:

http://parentalalienationinfo.com/2012/09/17-strategies-for-combating-parental-alienation-syndrome.html