Final answer:
When inserting a rigid-tip catheter into the mouth, it should be inserted until the tip hits something and stops.
Step-by-step explanation:
When inserting a rigid-tip catheter into the mouth of a patient, it should be inserted until the tip hits something and stops. This indicates that the catheter has reached the desired location. It is important not to insert the catheter further than necessary to avoid causing any damage or discomfort to the patient.