Holding a remote to direct the visual, he showed a run play with the Titans backed up near their own end zone, during a segment on the in-house television show Texans Extra Points this weekend.
"What he does is he sets the edge," O'Brien says. "Watch how he hits the tight end. Hits him right underneath the chin. Does a good job of setting the edge, funnels the back inside and then makes the tackle himself. Setting the edge allows J.J. Watt to get to the play, allows Vince Wilfork to get to the play, but they didn't even need to get there because Whitney made the tackle himself."
Mercilus lined up on the left side of the defense for the play, which isn't normally where the Texans play him.
The Texans have used a rotation of John Simon, Mercilus and Jadeveon Clowney at outside linebacker. Though both Mercilus and Clowney have been used primarily as right outside linebackers, the Texans would like to diversify their roles.
"Just because both of those guys have predominately played on the right side, I don’t think that is necessarily their strongest position," linebackers coach Mike Vrabel said. "I try to tell them the left tackles are the ones that make the most money, so if it were me, I’d try to rush somewhere other than the best player on the offense. That was always my theory. I think, hopefully, they can buy into that."
This season Simon has played 308 snaps, primarily on the left, Mercilus 324 total and Clowney 270. Clowney has played in seven of the Texans' eight games, and only played part of the first half against the Tennessee Titans as he suffered a back injury during it.
In Clowney's absence Mercilus gets most of his opportunity and produces the most. Mercilus played 208 snaps at right outside linebacker or right defensive end, and all of his 5.5 sacks have come from that side. All of those sacks have come while Clowney was not playing. When Clowney plays, the majority of Mercilus's snaps have come on the left side, though his playing time decreases significantly.
"I don’t want to say it’s difficult," Mercilus said. "It’s pretty much the same thing on both sides. Of course I’m probably a little more comfortable on the right side, which it shows, but I still try and get work on the left side and just try and be as comfortable as I can be."
Being comfortable is something Clowney has also worked on in different ways.
When healthy, Clowney has been better than his statistics suggests, but he's been far more productive from the right end position than anywhere else. In his 112 snaps at right end, Clowney has notched his only sack, one forced fumble and two pass breakups. He was an end, not a linebacker, in college, and is sometimes more comfortable with his hand on the ground than standing up.
As the Texans work through the different skill sets they have with each of their players, they could be finding ways to get Mercilus on the field more, even when Clowney is healthy enough to play.
"I think what we have to do is, we have to find situationally where guys can help us each down and distance," Vrabel said. "If it is third down, we move some guys around. I think some guys are comfortable different places. ... We just have to continue to find out who gives us the best chance to win on first down, second down and third down."