How to add quality control item(s) in survey with mainly Matrix Tables?

Hello everyone,
I am looking for some advice. I have a survey that at the beginning has some demographic questions and then the rest is images with Matrix Tables underneath (each column's heading is 1,2,3,4, or 5, with two labels at the ends, "not descriptive" and "descriptive"). I also intend to use Amazon Mechanical Turk for the subjects. However, I have read that when using Mechanical Turk one should add quality control items/questions (ex. "I have never brushed my teeth") to make sure the subjects are not mindlessly completing the survey in order to get paid. It is suggested that the question is in a similar format to the nearby questions so that it is harder to detect. So, simply adding a single Multiple Choice question or a Text Entry question wouldn't be good because it would stand out even to the mindlessly person.
I was thinking of adding a few scattered statements that say something like "one+one" or "one+three" and hopefully the subjects understand to select the second or fourth radio button, respectively...
Any tips on how to add a quality control question(s) for a survey with mainly Matrix Tables?
Thanks in advance!