A dodman or a hodmandod or hoddy-doddy is a snail. (I've used the word in my writing.) The OED is puzzled, but suggests a connection with "dod," which is Northern dialect for a roundheaded hill.

Reduplication" is the linguistic term; and "ablaut reduplication" for words like "chit-chat" and "riff-raff." The vowels have to go high to low in English: you wouldn't say "knack-knick."

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