It sometimes happens that a cavalry model will be riding a stupid creature, for example a Dark Elf riding a Cold One. If a rider's mount is stupid then he will have to test for stupidity at the start of his turn, but the rider's Leadership characteristic is used rather than that of the mount. If the test is failed the rider is obliged to hang on while the creature behaves in whatever bizarre manner the rules dictate, but the rider can fight normally if he gets the opportunity.