Please choose the correct ending to complete the given sentence: Pets and Animals: [header] How to diagnose patellar luxation in shih tzus [title] Look for skipping on the back leg. [step] A typical sign of patellar luxation is when the dog skips on a back leg. He may be perfectly mobile and not in pain, but every now and again he skips a step.

Ending1: [substeps] Note: a forward leg with patellar luxation can be measured in meters. A front leg with patellar luxation could be measured in inches. Ending2: However, this skipping doesn't mean your dog can't move. You can observe any skips your dog frequently forgets. Ending3: This is a completely normal way of crossing the joints. [title] Examine your dog's rump. Ending4: He may also carry a back leg for several steps before putting it back down again. [substeps] This is due to the mechanical locking of the knee joint due to the faulty anatomy.

Answer format: ending1/ending2/ending3/ending4