The Threat: How the FBI Protects America in the Age of Terror and Trump by Andrew G. McCabe:
The two people we sent to see Flynn were accomplished, seasoned agents. After the interview, they came back to my office and described it to a small group of us. They said that Flynn had a very good recollection of events, which he related chronologically and lucidly. They did not feel he showed any outward behavioral signs of deception. He did not appear to be nervous or sweating. Not looking side to side. Displayed none of the mannerisms commonly associated with dissembling or lying. They said he related his comments in what appeared to be a very credible fashion.
However, what he said was in absolute, direct conflict with the information that we had.