Behaviors and opinions of single individuals may be influenced by the dynamics operating within the groups where they interact. Likely, this influence is stronger when uncertainty characterizes the decisional stage . The conformity to common behaviors has been explained originally in ethology by the selfish herd theory as an attempt to reduce the predation risk . In human environment, the herd behaviors may take place in several situations and may affect deeply large groups of population. This is the case, for example, of the so called boom and bust phases in the stock markets. An explanation of the molding of a common decision (or opinion) within the financial markets has been given by the thought contagion theories, whereby single investors decide their operations by following the trend of the market.