When observing a 4-month-old infant, which finding would concern the nurse the most?

The concern regarding the finding that the infant's head lags when pulled from a lying to a sitting position relates to developmental milestones. By the age of 4 months, infants are expected to have developed certain motor skills, including adequate head control. Typically, they should be able to hold their head steady and show diminishing lag when being pulled to a sitting position. An excessive head lag at this age could indicate potential developmental delays, particularly concerning the strength and coordination needed for future motor activities.

In contrast, the other findings are considered more typical for a 4-month-old. The head turning in response to sound demonstrates auditory response and developing cognitive function, while drooling is common as infants begin to explore objects and develop oral motor skills even if they are not teething yet. The inability to focus on a toy held close to the face could raise some concern, but it is less alarming than the significant head lag expressed in the scenario because visual tracking can develop at varying rates. Overall, the head lag presents a more pressing concern regarding the infant's overall development.