rarity

found object, objet trouvé

curiosa, ephemera, virtu (or vertu)

marvel, prodigy, rara avis, rare bird, wonder

abnormality, anomaly, freak, monster, monstrosity

malformation, mutant, mutation

curiosity, peculiarity, singularity

accident, bizarrerie, phenomenon, quirk, vagary

distortion, kink, mutation, variation

difference, disparity, inconsistence, inconsistency

error, mistake

contradiction, paradox