_______________ to her superstitions, the mumpsimus irrationally avoided black cats.

The correct option is clinging.

Step-by-Step Explanation:

1. Analyze the Sentence Structure and Meaning:
The sentence describes a "mumpsimus" (a person who obstinately clings to an incorrect belief or practice) who irrationally avoids black cats due to their superstitions.
The missing word at the beginning of the sentence needs to describe the relationship between the person (the mumpsimus) and their superstitions.

2. Evaluate the Options:
- clinging: To "cling" to a superstition means to hold onto it firmly or refuse to let it go. This perfectly matches the definition of a mumpsimus, who obstinately holds onto irrational beliefs.
- falling: "Falling to her superstitions" is grammatically incorrect in this context; "falling back on" or "falling prey to" might be used, but "falling to" does not fit.
- loosening: If she were loosening her superstitions, she would be letting go of them and would be less likely to irrationally avoid black cats.
- dropping: Similarly, if she were dropping her superstitions, she would be discarding them, which contradicts the behavior of irrationally avoiding black cats.
- flipping: "Flipping to her superstitions" does not make semantic or idiomatic sense here.

3. Conclusion:
Therefore, the word clinging is the grammatically correct and contextually logical choice to complete the sentence.