Purpose or Case Report: Children, especially toddlers, are the most frequent victims of foreign body (FB) ingestion because of their natural curiosity, tempting them to put everything into their mouths. Anything within arm’s reach is fair game, from simple coins to the more dangerous button batteries and magnets. This study aims to provide a thorough review of plain radiographic findings of a myriad of foreign bodies (FBs) and associated complications. With the “Rule of 3–5”, we aim to help radiologists and clinicians develop a rationale and systematic approach in managing FB ingestions.
Methods & Materials: A curated number of items were compiled to demonstrate the vast range of ingested objects. Items included categories such as food, wood, plastic, sand, chalk, crayon, playdough, glass, metal and magnets. The items were placed on cardboard in order of expected radiographic densities from radiolucent to radiopaque to radiodense and plain radiographic images were obtained. The images were post-processed to least contrast and maximum brightness to improve visualization and characterization of different FBs.
Results: On plain radiography, most FBs are visible to varying degrees depending on density. Lucent objects such as food, wood and plastic can be delineated by adjusting contrast and brightness. High-density, radiopaque items were readily visualized and better characterized by changing the contrast and brightness.

Although the majority of ingested FBs pass the gastrointestinal (GI) system spontaneously, some require emergent intervention due to the triple threat of perforation, SBO and morbidity. These emergencies can be remembered by the "Rule of 3–5”: All long, linear or sharp objects measuring 3–5 cm in length; round, oval or polygonal objects measuring 3–5 cm in diameter; and multiple magnets or button batteries 3–5 in number require emergent attention.
Conclusions: Plain radiography from the level of the adenoid to anus is the best initial choice of imaging because of its easy availability, portability and ability to visualize objects of different densities. “Intelligent neglect” is suggested and uneventful expulsion is expected for all FBs, except those that fall within our “Rule of 3–5,” which pose a triple threat and require emergent GI/surgical consultation. Further evaluation with upright/decubitus imaging to exclude free air and SBO or CT may be performed as clinically indicated.