In most cases a cough impulse is felt. Gentle pressure is applied to the lump and the patient is asked to cough. If an impulse is felt this is due to increased abdominal pressure being transmitted into the hernia. In cases where the neck is tight and the hernia irreducible there may be no cough impulse. This can lead to failure of diagnosis and is typical of femoral hernia where lack of an impulse leads the clinician to misdiagnose a lymph node.