In the Fringe episode Unleashed, Walter recalls a song that he used to sing to his dog Rufus (which suffered from night terrors. )
The song he sings is called "Van Amburghs Menagerie", a popular song in the late 19th century about a menagerie (traveling zoo.)
Here are the lyrics that Walter sings, as he goes to confront the monster in the sewer:
Van Amburgh is the man, who goes to all the shows
He goes into the lion's cage, and tells you all he knows;
He sticks his head in the lion's mouth,and keeps it there a-while,
And when he pulls it out again, he greets you with a smile.
That Hyena in the next cage, most terrible to relate,
Got awful hungry the other day, and ate up his female mate;
He’s a very ferocious beast, don't go near him little boys,
For when he's angry he shakes his tail, and makes this awful noise.
Click here to read the full lyrics
BTW, Menagerie is also this week's Star Trek reference - the name of the only two-part episode from the original series.