Allen was back on the practice field 11 days after being cut at the end of training camp.
"This is a business," he said. "You've got to understand. You can't take anything personal. You take the punch, and you keep rolling. Bitterness doesn't get me anywhere, so here I am."
"One guy was healthy. The other guy really wasn't," Sparano said. "Allen's better right now."
Allen started 53 games for Miami from 2006 to 2009, then missed last season with a knee injury. Teammates in the secondary said they were glad to have him back.
"It's huge," safety Yeremiah Bell said. "He's a veteran guy who knows the game. He's a leader back there."
"You've always got something to prove," Allen said. "Always. I've felt like that since I set foot in this league, probably since I came out of the womb."
Copyright 2011 by The Associated Press