There is a saying that coming events cast their shadows before. (1) ______ it is not universally true. Something can happen within a second, and one may not (2) ______ it. (3) ______ some instances show that predictions based on certain signs have gone wrong. People generally say that natural calamities can be predicted by observing the animals. But what if animals are suffering from some disease and don’t show any signs before the event appears? They may fail to make peculiar sounds or actions about the events which are going to take place. (4) ______ some unnatural calamities that are likely to appear may forecast their shadows by some bad omens. (5) ______ we should not completely cancel out the possibilities that animals can sense certain unnatural happenings.

Select the most appropriate option to fill in blank number 4.

To determine the most appropriate connector for blank number (4), let us analyze the semantic relationship between the sentence containing the blank and the preceding context.

The passage discusses the predictability of coming events. The sentences leading up to the blank argue that natural calamities are not always predictable, specifically highlighting that animals might fail to show signs or make peculiar sounds if they are diseased.
Sentence (4) states: "______ some unnatural calamities that are likely to appear may forecast their shadows by some bad omens." This sentence introduces an additional point or a transition to another aspect (unnatural calamities forecasting their shadows), which adds to or stands alongside the previous discussion about the limitations of natural calamity predictions.

Let us evaluate the given options:
1. Therefore: Used to introduce a logical result or consequence. The fact that unnatural calamities may forecast their shadows is not a direct consequence of animals failing to show signs of disease.
2. Secondly: Used to introduce a second point in a list. While it introduces a new point, the text has not established a formal sequence (like "Firstly") to warrant "Secondly" here.
3. Besides: Means "in addition to" or "moreover". It is used to introduce an additional point or argument that supports or adds to the discussion. Here, it adds the point about unnatural calamities and bad omens to the discussion on predictability.
4. Despite: Means "in spite of" and is a preposition, which would require a noun phrase rather than a clause starting with "some unnatural calamities...".

Thus, "Besides" is the most appropriate transitional word to introduce this additional point, linking the sentences logically.

Therefore, the correct option to fill in blank (4) is Besides.