We conduct a manual error analysis of the CoNLL-SIGMORPHON 2017 Shared Task on Morphological Reinflection. In this task, systems are given a word in citation form (e.g., *hug*) and asked to produce the corresponding inflected form (e.g., the simple past *hugged*). This design lets us analyze errors much like we might analyze children’s production errors. We propose an error taxonomy and use it to annotate errors made by the top two systems across twelve languages. Many of the observed errors are related to inflectional patterns sensitive to inherent linguistic properties such as animacy or affect; many others are failures to predict truly unpredictable phonological behaviors such as umlaut in Germanic, metaphony in Romance, and yers in Slavic. We also find nearly one quarter of the residual “errors” reflect errors in the gold data.