Each and every palladium sample loaded/reloaded either with hydrogen or deuterium was observed to fog radiographic films kept in its close proximity in air. Strangely, even with ten layers of black paper (thickness ≃63 mg/cm2) as a filter between film and sample, fogging was observed. On the other hand, no fogging could be observed even when thin beryllium foil (≃1.4 mg/cm2), three layers of transparent polyester foils (≃10 mg/cm2), or thin aluminizedpolycarbonate (0.3 mg/cm2) were employed as filters. Several experiments have been performed to identify the phenomenon responsible for fogging. These experiments appear to rule out any of the known mechanisms, suggesting a new, strange, and unknown phenomena.