Bart perked up almost immediately, his entire body language changing, picking up and straightening as he beamed at Grampa. When Grampa said things were going to be alright, Bart believed him in a way that he wouldn't, couldn't, believe anyone else, except for maybe Grandma Iris. And Grampa said they'd go see Grandma Iris too.
Bart was not at all fond of tests, academic or other wise, and after spending the early part of his life as-- basically-- a science experiment, he wasn't too fond of being tested, but he forgot about all of that since it was Grampa. Bart darted from the chair at super speed to the lab equipment from which he plucked a cotton swab and swabbed the inside of his cheek, then sped back over to Barry, holding the swab out. If the kid was crazy, he sure was confident about it.