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A barking dog seldom bites.
Literal
Bark dog [topic-は] seldom bite-at thing [topic-は] not.
噛み付く ('to bite at, to snap at') compounds 噛む ('bite') with 付く ('attach'), giving a more vivid, aggressive flavor than the bare 噛む — it pictures a dog lunging and clamping on. The ~ことはない pattern ('there's no occasion of, never does') negates the action as a general truth. The English proverb 'a barking dog seldom bites' has a near-equivalent in Japanese: 吠える犬は噛まない.