The researcher shows a child cards with drawings of imaginary animals, and teaches the child a nonsense name for the animal.
The researcher says, "This is a wug. Now there is another one. There are two of them. There are two wugs."
Very young children are baffled by the question and are unable to answer correctly, sometimes responding with "two wug".
Children aged 4-5 test best in dealing with the voiced alveolar fricative /z/ after a voiced consonant; they do almost as well with the voiceless alveolar fricative /s/.
The Wug Test also includes questions that explore a child's understanding of verb inflections and the possession.
Additional items were designed to investigate children's ability to handle common derivational bound morphemes such as the agentive -er. (a man who works = worker)