Sentence:  But when, obedient to the mode / Of panegyric, courtly ode / The bard bestrides, his annual hack, / In vain I taste, and sip and <WSD>smack</WSD>, / I find no flavour of the Sack. 
Meaning of the word marked with <WSD> tags:  To wetly separate the lips, making a noise, after tasting something or in expectation of a treat.