When you interject your opinion into a conversation that two other people are having, this is a time when you interpolate.
When you insert words or letters into text, this is an example of a time when you interpolate.
In verse 74, the second line is clearly interpolated.
Origin of interpolate
- Latin interpolāre interpolāt- to touch up, refurbish from interpolis refurbished pel-5 in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition