Hypothesis testing and anomaly explaining

An experimenter who tests a hypothesis and observes an anomaly that conflicts with his knowledge and views, normally reacts by suspecting some sort of mistake. When he has excluded this possibility, his second sensible reaction is to find an ad hoc interpretation to explain the anomaly. When his favorite interpretation is interesting, probable, simple, elegant and testable enough, he can experiment to verify this explanation as a new hypothesis, independently from the anomaly. This article describes how a scientific investigation walks on two legs: one leg of hypothesis testing and a second leg of anomaly explaining.