Sometimes the notes are ferocious,
Skirmishes against the author
Raging along the borders of every page
In tiny black script.
If I could just get my hands on you,
Kierkegaard, or Conor Cruise O'Brien,
They seem to say,
I would bolt the door and beat some logic into your head.
Other comments are more offhand, dismissive -
"Nonsense." "Please!" "HA!!" -
That kind of thing.
I remember once looking up from my reading,
My thumb as a bookmark,
Trying to imagine what the person must look like
Who wrote "Don't be a ninny"
Alongside a paragraph in The Life of Emily Dickinson.
Students are more modest
This is the first of two specific marginalia that the speaker of the poem recalls in the poem, the later one encompassing the final two climactic stanzas. 
 These lines also establish the speaker as a thoughtful reader, pausing to reflect not only on the books he is reading, but their marginalia as well
Marginalia