Final answer:
The irregular plural noun in the sentence is 'knives'.
Step-by-step explanation:
The irregular plural noun in the sentence is knives. In English, most plural nouns are formed by adding -s or -es to the singular form of the noun. However, irregular plural nouns do not follow this pattern and have their own unique forms. For example, the singular form of 'knife' is 'knife', but the plural form is 'knives'. Other examples include 'sheep' (singular) and 'sheep' (plural), 'child' (singular) and 'children' (plural), and 'mouse' (singular) and 'mice' (plural).
Learn more about Irregular plural nouns