Triggering feedback layer if text entry field contains certain words

Hi there, 

I am building a "restating exercise" where I want the learner to practice rephrasing a statement using a data entry text field. The statement may not contain certain words, such as "don't" or "stop". 

 

So, I want a feedback layer to be triggered once the learner is finished entering their text in the text entry field, IF their text contains certain words. 

 

Help please. 

 

Thank you:)

 

Susann