And full-grown lambs loud bleat from hilly bourn;
This is so dark it’s almost morbid.
Lambs are never meant to be ‘fully-grown’. When they reach this point, they either a) become sheep or b) become:
The ‘bleating’ here is almost a call for help or death wail. It’s not a pleasant aural reference at all. Keats is giving in to morbidity here, the subtext of the bleating lambs being his own fear of death. It’s sad, and desperate.
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