The first word of the title, unusual, captures the theme of this article. The entities discussed here: fat embolism, tumor embolism, venous air embolism, and amniotic fluid embolism, as well as other unusual embolic events are uncommon disorders that occur in specific circumscribed clinical settings. We have attempted to provide a cognitive jolt to remind the reader to consider these unusual events in appropriate differential diagnoses. No laboratory test, physical finding, or patient complaint will yield a timely diagnosis. Yet, these entities can be acutely life threatening; swift recognition is imperative. Timely and effective therapy rests on the clinical certainty that a test is not likely to establish. It is, perhaps, the greatest demand placed upon the agile clinical mind--to think of it!