What is the difference between normal and fast retraction ?

[Anders L Madsen]

When performing fast retraction inference, the evidence potentials are multiplied onto the clique potentials during propagation (as opposed to before propagation, in normal inference). If this is done correctly, the resulting potential on a set V of variables will be the marginal probability for V given evidence on all variables except the variables in V.
This can be useful to identify suspicius findings. If the observation made on a variable has a very small probability, then quite likely something is wrong with the observation.