Wee, sleekit, cowrin, tim'rous beastie
O, what panic's in thy breastie!
Thou need na start awa sae hasty
Wi' bickering brattle!
I wad be laith to rin an' chase thee
Wi' murd'ring pattle!
I'm truly sorry Man's dominion
Has broken Nature's social union
An' justifies that ill opinion
Rough English translation: 
 Small, crafty, cowering, timorous little beast, O, what a panic is in your little breast! You need not start away so hasty With argumentative chatter! I would be loath to run and chase you, With murdering plough-staff. 
 Burns, while plowing his field, has turned over the nest of a mother mouse. This poem is his apology for doing so; he assures the mouse he didn’t mean to disturb her and that she need not fear him. The impact of this is strong; Burns has the imagination to address the mouse in the second person as if he is talking to her and understands what the creature feels, and the compassion to identify with its suffering. 
 Burns' launches him poem with lush, memorable adjectives to describe the mouse. One student commented that the words are ‘so expressive you can taste them!’. Not only is this line wonderfully effective as a hook, it is one of Burns' most famous lines. 
 Note also that the first three lines and the fifth line are  consonantly  rhymed. The fourth and sixth lines are perfect rhymes. This gives the poem drama and emphasis. 
 
 Also note the  alliterative  and  plosive  ‘b’s and 'p’s, which, if spoken with exaggerated expression, make this work so well in performance. 
 Burns introduces his mouse using the diminutive ‘beastie’, a mark of almost affection.
To a Mouse