We propose a new approach to falsify causal discovery algorithms without ground truth, which is based on testing the causal model on a variable pair excluded during learning the causal model. Specifically, given data on X,Y,Z = X,Y,Z1,...,Zk, we apply the causal discovery algorithm separately to the ’leave-one-out’ data sets X,Z and Y,Z. We demonstrate that the two resulting causal models, in the form of