It's important to keep one's wits about one in a dangerous situation.

He always has his wits about him.

She had her wits about her and quickly found a solution to the problem.

She is having her wits about her while solving the puzzle.

The document witnesseth the agreement between the two parties.

She witnesses the crime.

He called upon the witnesse to testify in court.

He witnesse the crime.

The crime scene was witnessless, making it difficult for the investigators to gather evidence.

The witnesser testified in court.