Which of the following defines the highest degree of intrusion during a search?

The correct answer is cavity penetration, which indicates the highest degree of intrusion during a search. This level of search involves physically entering and examining a person's body cavities, which is considered a highly invasive act.

Cavity penetration requires compelling justification, often necessitating a warrant or exigent circumstances, due to the significant privacy interests at stake. Such searches are closely scrutinized by courts to ensure they do not violate constitutional protections against unreasonable searches and seizures.

The other methods mentioned, such as looking in, manipulation, and reaching in, are less intrusive in nature. Looking in refers to observing items from a distance without physical engagement, while manipulation generally involves handling items without invasive measures. Reaching in suggests limited physical contact but still doesn't equate to the severity and privacy infringement associated with cavity searches, which clearly outlines why cavity penetration is recognized as the most intrusive form of search.