Imagine asking your teenager the following, "Who are going out with tonight?", or "Where will you be going?". Typically the response is "with friends" or "nowhere special", yet you instinctively know that trouble is a-brewing. You can tell by the manner in which they answer.
Intuitively, you know that hestitation means trouble. Reseachers have found that a truthful hesitation is 0.5 seconds, whereas the average hesitation for liars is 1.5 seconds. Technology today can utilize algorithms to meaure this hesitation against a baseline of always true questions.
...a decrease in rate often indicates that the subject is editing information from the account, or fabricating information within the account. Both of these mental activities (editing and fabrication) require time and to buy time, the subject slows down his response rate.