We have already seen how “spider” meets these criteria. Remember the lines from Shakespeare: “Golden lads and girls all must, as chimney sweepers, come to dust”? “Must” as an echoic stimulus might also strengthen “rust, crust, lust”—each of which would have very different effects upon the listener.
Controlling variables with the following features:
The response being analyzed is also controlled by a main thematic source
It also controls other response forms
The other response forms would have a different effect upon the listener
Whether the relationship between the secondary source and the response is formal or thematic