This normally happens in the facial area. Very often a blood vessel that has burst is easily visible, as the blood vessel is situated under a transparent layer of skin. These blood vessels can either be bright red or dark in appearance. The burst blood vessels can cause pain, if they come in contact with anything.
A couplet is a pair of lines of metre in poetry. Couplets usually comprise two lines that rhyme and have the same metre. A couplet may be formal (closed) or run-on (open). In a formal (or closed) couplet, each of the two lines is end-stopped, implying that there is a grammatical pause at the end of a line of verse.
The poem also rhymes, and therefore it has a rhyme scheme. In this poem, the rhyme scheme is: AABB. This means that in each four-line stanza, the first two lines rhyme (their rhyming sound is indicated with an A), and the last two lines rhyme (B). These rhyming pairs are called couplets, probably because they are like little verbal couples.