Julio Jones of the Atlanta Falcons rushes against the Houston Texans in their pre-season game. (Thomas B. Shea/Getty Images)

Ever wonder what the inside of a knee looks like? The third episode of the NFL’s five-part “Hard Knocks” series on HBO began Tuesday night with a behind-the-cartilage look at Marquis Spruill’s left knee anterior cruciate ligament reconstruction surgery and it was gnarly.

But that wasn’t the craziest thing viewers saw. There was also:

Running back Steven Jackson doing arm curls with 125-pound dumbbells like it was no big deal.

Wide receiver Roddy White scaring fans with his sloth-like reflexes when he repeatedly failed at the “dollar game,” a party trick where one person drops the bill between someone else’s fingers while that person tries to pinch it in mid-air before it falls to the ground.

Bryan Cox sitting down all the defensive linemen to show them a slide show of his family, including his pretty young daughter, who the defensive line coach colorfully warns players to not befriend on Instagram.

Quarterback Matt Ryan telling a joke that partly relied on thinking “duct tape” was called “duck tape.”

Safety William Moore throwing down an absolutely amazing freestyle in the training room.

Harry Douglas putting on a clinic in bowling for fellow wide receivers Roddy White and Julio Jones. “I’ve been bowling that way since I was 13,” Douglas says when questioned about his high-arcing throws, which result in the balls thudding onto the lane before surprisingly hitting strikes. Well, until that one time when he threw the ball into the adjoining lane’s gutter…

Backup quarterback T.J. Yates practicing his quarterback calls in whispers… while sitting in a room by himself.

The NFL’s edit of Houston Texans defensive end J.J. Watt entering the Falcons-Texans joint practice field looking very much like the Terminator.

And finally, tight end Levine Toilolo singing a ukelele version of Biz Markie’s “Just a Friend” to his teammates in a hot tub.