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 5.

The correct answer is Therefore.

To determine the most appropriate option to fill in blank number (5), let us analyze the context of the paragraph:
The passage discusses the predictability of coming events through certain signs or animal behaviors. It highlights limitations (e.g., animals might be sick and fail to show signs before an event). However, the sentence before blank (5) states: "some unnatural calamities that are likely to appear may forecast their shadows by some bad omens."
Blank (5) is followed by: "______ we should not completely cancel out the possibilities that animals can sense certain unnatural happenings."

The relationship between the preceding sentence and the final sentence is one of logical consequence or conclusion. Since some calamities do cast warning signs (omens), it follows logically that we should not entirely dismiss the ability of animals to sense these occurrences.
Let us evaluate the given options:
1. Therefore: Used to introduce a logical transition, conclusion, or result of the preceding statement. This fits the context perfectly.
2. However: Used to introduce a contrast. This is incorrect because the final sentence supports the idea of the preceding sentence rather than contradicting it.
3. Nevertheless: Means "in spite of that" or "nonetheless," which is used to show contrast or concession. This is incorrect here.
4. Moreover: Used to add extra supporting information. While it adds info, it does not capture the direct cause-and-effect relationship as well as "Therefore" does.

Thus, Therefore is the most suitable cohesive device to connect the two thoughts logically.