Crack propagating direction and front shape can be significantly affected when encountering stress wave perturbations, which changes fracture paths and fracture surface roughness. Here, we study the dynamic cleavage behavior of (001) silicon single crystal wafers under bending tests. We show that the crack propagates preferentially along the (110) cleavage plane under pure bending load regardless of the crack propagating velocity. However, when fracturing under bending load with contact perturbations, shear waves emit from the line-contact and deflects the crack front onto the (111) cleavage plane upon interaction which generates secondary Wallner lines. Yet, the crack propagation along (111) plane is not permanent as it recovers to the (110) plane after a certain length relating to the crack velocity, which reveals that the cleavage along (110) plane is energetically favorable and conforms to the principle of minimum energy dissipation even in high-speed fracture process. In addition, it is found that, during the crack growth on the (110) cleavage plane, the fracture surface is mirror-like and crack front shape can be approximated with a quarter-ellipse at the crack velocity lower than 2600 m/s. Above this velocity, the crack front shape involves a local curvature jump which is velocity-dependent. We highlight that special elastic waves occur from the curvature jump position, and we suggest that they are front wave resulting from a local fracture energy fluctuation. These waves contain the out-of-plane component that kinks the crack front to leave special surface undulations, which obviously alter the surface roughness.