In the Four-Letter Words Brain Exercise, why are some words not accepted?

Certain words may not be recognized in the HSI Blue Ocean Brain Exercise, Four-Letter Words.

If your organization's HSI Blue Ocean Brain experience includes Brain Exercises, you may be familiar with the Brain Exercise, Four-Letter Words. This Brain Exercise looks up words in a large dictionary, but there is a possibility that some words may not be in the dictionary. Technical terms, proper nouns, slang, and non-English words may not be accepted.