People fumble around with their words a lot when they're lying. In fact, a liar often adds words so they can truthfully answer questions by obscuring the meaning. Psychology Today points to a method to catch a liar where you can react to words called tag qualifiers.
Image remixed from Steven Isaacson.
The words include "this", "that", "these", "those" and "though". Tag qualifiers work because one can't exist without the other. If someone says "that", then there must be a this. So, if someone says, "I didn't do that", they have to know what "that" means, or you could follow up with the question, "If you didn't do that, what did you do?" Using these words, a liar can actually tell the truth but not the whole truth. Psychology Today offers this example:
TIMMY'S MOTHER: Your teacher called and said that during recess you ran up to Vickie and pulled her hair causing her to fall down and hurt her head.
TIMMY: She's lying. I didn't do that.
Timmy used the Tag Qualifier "that" to give the illusion of truth. Timmy did pull Vickie's hair causing her to fall down and hurt her head, but he did not run up to Vickie and pull her hair, he walked up to Vickie and pulled her hair. Since his mother's description of the event was not exact, Timmy could use the Tag Qualifier "that" to maintain the illusion of truth. However, Timmy cannot use the word "that" without having considered at least one alternate action.
Essentially, if you think someone is lying to you, listen for those tag qualifiers. If the words aren't attached to anything, you can gently probe a bit more to get to the bottom of a lie. Head over to Psychology Today for a few more example conversations.
Catch Liars Using the This/That Trap [Psychology Today]