= "sneak"の過去・過去分詞。
Wiktionaryには、
Etymology[edit]
The irregular form snuck originated by analogy with struck for the past of strike. Snuck was originally limited to a few dialects, but is now very widespread (especially in American English) and is recognized by most dictionaries. The word is now one of the best examples of irregularization of a regular verb, along with dove.
とある。もともとの過去形＆アメリカ以外ではもちろん"sneaked"なんだけど、一部の方言が広く使われるようになって辞書に載った例。dive/doveもそうなんだそう。
方言も皆が喋れば標準語。
