ORIGINAL    Lying on top of the intestine, one can make out a small white thread.

What is it that is "lying on top of the intestine"? Surely not the observer, the "one." But that is what the sentence says.

    REVISION    One can make out a small white thread lying on top of the intestine.

Now the modifier "lying" is as close as possible to the word it modifies, "thread." Writing from A to Z provides several more examples of misplaced modifiers on pages 373-375.

Dangling modifiers occur when the action expressed in a participal is not attributable to the correct noun or pronoun.

    ORIGINAL    Claiming to hate lies, it is ironic that Marlow ends his account of Kurtz by lying to the Intended.

What noun really contributes the action expressed in the participal "claiming"? Not the vague "it" that begins the main clause of the sentence. There are at least two possible ways to revise.

    REVISION #1    Claiming to hate lies, Marlow ironically ends his account of Kurtz by lying to the Intended.

Now Marlow is the subject of the sentence, and the action of the participal "claiming" is clearly attributable to him. Introductory participial phrases always act to modify the grammatical subject of the sentence, and dangling modifiers occur when the subject can not perform the action expressed in the participal.

    REVISION #3    Marlow claims to hate lies but ironically ends his account of Kurtz by lying to the Intended.

This revision eliminates the participal altogether by expressing the action in a verb rather than a participal.