A twinkle in the eye. That subtle signifier of mischief within. It gives Paddy Lowe away as one of the good guys, even as he carries - lightly - the mantle of technical greatness. The warmth of his greeting at Williams's Grove HQ, a readiness to chat. It's disarming in one so accomplished.
This, after all, is the man whose technical leadership (in tandem, it must be noted, with engine boss Andy Cowell) helped Mercedes to a period of consummate domination from 2014-16. And one whose CV encompasses years at Williams during its 1990s glory days, then McLaren when it was last a frontrunner.
Lowe has been at the cutting edge of seven successful world title campaigns, with three different teams, making him one of a tiny elite band of rock-star tech titans active among the F1 tribe. He, along with Adrian Newey, James Allison and Rory Byrne, plus Cowell and - maybe - Ferrari's emerging Mattia Binotto, are those considered sufficiently eminent to be able to make a difference by virtue of their presence, nous and method.