A patient exhibiting catatonia is most likely to show:

A patient exhibiting catatonia is most likely to show a lack of movement or response. This condition is characterized by a marked decrease in responsiveness to the environment, which can manifest as immobility, mutism, or an inability to engage in normal motor functions. The behavior can range from a complete lack of movement to stereotyped movements repeated over and over. This immobilization and lack of responsiveness are key features of catatonia, making it distinct from other conditions that might involve mood changes or increased levels of activity.

In contrast, excessive talking, sharp mood swings, and extreme hyperactivity are not characteristic of catatonia. These behaviors align more closely with other psychiatric disorders or conditions like mania or certain mood disorders but do not represent the typically observed symptoms in catatonia. Therefore, the defining symptom of catatonia is indeed the lack of movement or response.