Title: Exploring interactions between modalities for deepfake detection. Abstract: As face forgery techniques have become more mature, the proliferation of deepfakes may threat the human society security. Although existing deepfake detection methods achieve a good performance for in-dataset evaluation, it still remains to be improved in the generalization abiltiy, where the representation of the imperceptible artifacts plays a significant role. In this paper, we propose an Interactive Two-Stream Network (ITSNet) to explore the discriminant inconsistency representation from the perspective of cross-modality. Specially, the patch-wise Decomposable Discrete Cosine Transform (DDCT) is adopted to extract fine-grained high-frequency clues and information from different modalities are communitcated with each other via a designed interaction module. To perceive the temporal inconsistency, we first develop a Short-term Embedding Module (SEM) to refine subtle local inconsistency representation between adjacent frames, and then a Long-term Embedding Module (LEM) is designed to further refine the erratic temporal inconsistency representation from the long-range perspective. Extensive experimental results conducted on three public datasets show that ITSNet outperforms the state-of-the-art methods both in terms of in-dataset and cross-dataset evaluations.