Weak gravitational lensing distorts the shapes of background galaxies, and this distortion can be decomposed into two components: E-modes (gradient-like patterns) and B-modes (curl-like patterns). In the absence of systematic errors or higher-order lensing effects, standard gravitational lensing from scalar density perturbations should produce predominantly E-modes, with B-modes arising only from special configurations like multiple lens planes or rotational effects. However, observations of cosmic shear reveal an excess of B-mode power at various angular scales beyond what Lambda-CDM predicts from known sources, and the B-mode signal shows unexpected spatial patterns and scale-dependence (Schneider et al. 2002; Kilbinger et al. 2013). Lambda-CDM struggles with this tension because the observed B-mode excess cannot be fully explained by observational systematics (point spread function errors, shape measurement biases) or known astrophysical sources (intrinsic alignments, source clustering), suggesting either that the gravitational lensing is being influenced by unanticipated mass distributions with significant rotational or vector components, or that the lensing geometry itself differs from the standard assumptions of purely scalar perturbations on smoothly evolving backgrounds.