Studies on L2 processing of Differential Object Marking (DOM) are scant and mostly focus on the animacy of the object. We investigated the interaction of three understudied factors in L1 and L2 processing of DOM: type of animacy (human vs. non-human animal), gender and number of the object (masculine vs. feminine, plural vs. singular), and morphological salience of the DOM marker (e.g., al bound/less salient vs. a unbound/more salient). Forty-three Spanish monolinguals and 81 English learners of Spanish (39 intermediate, 42 advanced) completed a self-paced reading task with subject relative clauses (RCs) containing DPs with singular and plural human or animal direct object nouns. Results showed that L2 learners' sensitivity to animacy hierarchy differences is possible in cognitively easy conditions (unbound DOM, masculine gender). These findings inform current L2 representational and processing models, and stress the value of examining multiple factors to fully understand the complexity of DOM.