You wouldn’t know it by looking at his often expression-less face, but Tim Duncan is actually a really funny guy. Occasionally, he even lets the world in on this secret. Here’s the San Antonio Spurs legend joking about his advanced age and lack of speed leading to a historic season on the defensive side of the ball. Per the Express-News: “At age 36, and in the midst of arguably the greatest run of shot-swatting in his Hall of Fame-bound career, Duncan says the secret behind his longevity as a defensive menace is twofold. ‘I’m old,’ Duncan deadpanned, ‘but I’m slow.’ [...] In his 16th season, Duncan has been offering up more rejections than a homecoming queen, totaling 173 in 65 games — all, as he likes to joke, without leaving the floor. Duncan’s average of 2.7 blocks per game ranks third in the league and puts him on pace for the best shot-blocking season by a 36-year-old in league history. Since the NBA began tracking blocks in 1973-74, no player Duncan’s age has come close to that number over a full season. New York’s Patrick Ewing averaged 2.6 blocks in 38 games of a lockout-shortened 1998-99 campaign. Duncan’s average of 3.2 blocks per 36 minutes, meanwhile, marks by far the highest rate of his career. Are we amazed yet? ‘I guess to some degree, I should say yes,’ coach Gregg Popovich said, ‘just because people in that stage of their career don’t do the things he’s doing.’ An eight-time member of the NBA’s All-Defensive first team, Duncan — who turns 37 on April 25 — is building a case to become the oldest Defensive Player of the Year in history. The eighth-leading shot-blocker of all time with 2,642, Duncan is the centerpiece of a Spurs team that ranks third in defensive efficiency, up from 10th last season. He has posted at least three blocks in a game 31 times this season, including a stretch of seven in a row in January. [...] Like a magician loath to reveal the technique behind his illusions, Duncan downplays the legwork that goes into his shot-blocking. ‘I just think I’ve tricked people into coming into a certain territory,’ Duncan said.”