Here are five observations from the first day of Texans' training camp on Thursday:

Watson excels in red zone

On a morning when the Texans worked on the red zone a lot, quarterback Deshaun Watson was sharp. He took quick drops, released the ball fast and put it where he wanted it to go. One of his pinpoint passes was to second-year tight end Jordan Thomas in the corner of the end zone. Watson's timing was impeccable. He threw the ball at the right time, floated it over the outstretched hands of the defensive backs and to Thomas, who got both feet inbounds for an impressive touchdown.

As coach Bill O'Brien kept pointing out in his interview session with the media, the players won't be wearing pads until Saturday. Still, Watson had a superb first day and impressed his coaches and teammates with his work in the end zone.

If the Texans are going to become a prolific offense, Watson has to be quick and crisp the closer they get to the end zone. He can't hold the ball, then take off and try to beat defensive players to the pylons. He must be more decisive in his third season because everything happens quicker in the red zone.

Watt participates in first practice

When players go on active/physically unable to perform list before training camp, it means they can't pass a physical. When they can, they'll be on the field. Defensive end J.J. Watt passed his physical, was removed from PUP and practiced.

Having a healthy Watt means everything to the defense, of course. At this time last year, he knew what he wanted to do coming off major surgery on his leg. He knew what he was capable of, but nobody knew for sure how Watt would play. He played great, finishing with 16 sacks.

Watt looked like an eager rookie Thursday. When he's on the field, there's a buzz on both sides of the ball. It benefits the young offensive linemen to go against Watt in one-on-one drills. Plus, he's always willing to work with other players on techniques and show them tricks of the trade.

If the Texans are going to win the AFC South again, Watt has to have another great season. At this point, nobody is doubting him.

Kalil impresses on first day

Left tackle Matt Kalil, signed as a free agent after being released by Carolina, has impressed his coaches and teammates. After missing two of the last three seasons with the Panthers, including last season with a knee injury, Kalil was brought along slowly in the offseason program. That strategy seems to have paid off.

Bill O'Brien said Kalil, 30 and entering his eighth season, has done an outstanding job of learning the system. He's smart, experienced and has ideal size (6-7, 315) for his position. If Kalil can continue to make progress and earn a starting job, it would give offensive line coach Mike Devlin flexibility with first-round pick Tytus Howard, who could start at left guard. Since the offseason program began, Howard has been learning both positions, and Kalil has been helping him.

Cornerbacks off to fast start

Two cornerbacks — veteran Bradley Roby and rookie Lonnie Johnson (second round) — missed time in the offseason because of injuries. Both were on the field for the first day of practice and making positive impressions.

Johnson (6-2, 213) has excellent size and speed (4.4s) for his position. He made a tremendous play during practice. On a pass intended for second-year receiver Jester Weah, Johnson left his feet and made a diving interception. Plays like that catch defensive coordinator Romeo Crennel's attention and will get Johnson more playing time.

Roby was able to participate in the last two practices of minicamp. He was going full speed in the first practice. He's supposed to start opposite Johnathan Joseph, but Roby has the experience and versatility to move inside, too. If Johnson performs well enough to earn playing time outside opposite Joseph, who's 35 and in his 14th season, Roby could play inside and compete with Aaron Colvin as the top slot corner.

How fast Johnson develops will play a key role in how the secondary plays against a Murderer's Row of quarterbacks over the first seven games of the season: Drew Brees, Nick Foles, Philip Rivers, Cam Newton, Matt Ryan, Patrick Mahomes and Andrew Luck.

Conspicuous by his absence

Outside linebacker Jadeveon Clowney wasn't at practice, of course, but it didn't mean he wouldn't be a topic of conversation. Clowney will play under the franchise tag when he reports before the first game at New Orleans and players get paid base salaries over 17 weeks.

When he was asked about Clowney, Bill O'Brien said all the right things about expecting him back, wanting him on the team and how valuable he would be to the defense.

If Clowney wants to maximize his value and get the contract he wants from the Texans or get them to trade him before next year's draft, he'll have to be more productive as a pass rusher. He's been working with former defensive ends Julius Peppers and Chuck Smith in Miami.

What Clowney should do is not wait for the week before the New Orleans game to report. He should report earlier to make he's in the best football condition possible so he won't get off to a slow start. Players who work out on their own and miss a lot of football conditioning are often susceptible to pulled muscles that cause them to miss playing time. Clowney should do everything possible to avoid that by reporting and letting the Texans get him into football condition before they play the Saints.