Normally Lowell would just toss the ball back to pitcher, Todd Jones. This time, though, he notices that neither Terrero nor Carlos Tosca, the third base coach, are looking at him, so he just keeps the ball in the glove, and saunters back towards third, just as though he'd already returned the ball to Jones. He never looks directly at Terrero, nor does he say anything. He just takes his position, albeit a bit closer to third than usual. Now it's Jones's turn for subtlety. First of all, he has to be quick on the uptake. If Jones is clueless, he's going to be standing there waiting for someone to throw him the ball, and the jig will be up. It's not like Lowell can tell him what's going on. He knows Lowell didn't return the ball, but he can't react to that in any way that would make someone suspect he doesn't have it. Perhaps Lowell gave him a quick glance. Whatever, things have to look normal. (The sad thing about hidden ball tricks is that the good ones are almost never caught on video, except perhaps the actual tag out, as in this case.)
Jones pretends he has the ball. This is harder than it sounds, because if he steps anywhere on the mound without the ball it's a balk, and the tying run scores. He has to figure out how to stall without stepping on the mound. If he'd been the starter, he could've just thrown a little tantrum behind the mound over the cheap hit he'd just given up, as starters are wont to do. Relievers, though, are supposed to be in control of their emotions. Also, if he looks too upset, there's a good chance that the catcher might decide to come out to the mound to calm him down. If that happens, the ump will call time, and the play with be toast. He picks up the rosin bag to dust his pitching hand, and motions to his catcher that he's fine.
Terrero, meanwhile, has been going over the situation with Tosca, blissfully unaware of what is going on three feet to his left. Tosca is also busy getting the signs for the next at bat. Craig Counsell at the plate is a good bunter, so there's the possibility of a squeeze play, and Tosca is looking to the dugout to see if it'll be called. Terrero and Tosca both figure that the reason that Lowell is so close to third is because of the potential squeeze.
So, Tosca is waiting to flash the signs. Counsell is standing at the plate, waiting for Jones to go to the rubber, and turns to look at Tosca. Lowell is standing a step inside the line, even with the bag. Now, Terrero makes his mistake, and starts to take a short lead off third. Immediately, Lowell takes one step to his right and applies the tag. The ump is right there, having figured out what was going on immediately. Terrero is out, and the threat is killed. It was a beautiful thing.
After the fact, both Terrero and Tosca admitted to being uneasy, like they were missing something. There's been only one other successful hidden ball play in this decade, and it was Mike Lowell who pulled that one off, too. The man has a gift.