The word "壳儿" is formed by taking the base character "壳", meaning "shell" or "husk", and appending the suffix "儿", which represents erhua, a phonetic alteration in Mandarin where the "r" sound is added to the syllable. This erhua modification typically conveys a colloquial, diminutive, or regionally specific nuance, resulting in a spoken variant often used in northern Chinese dialects.