A TSA officer will give the pet owner's hands an explosive trace detection swab to ensure there is no explosive residue on the owner's hands. After the screening process is complete, owners should return their pet to the travel carrier at the re-composure area away from the security checkpoint.
What is TSA doing when they swab your hands?
Also, TSA officers may swab your hands, mobility aids, equipment and other external medical devices to test for explosives using explosives trace detection technology.