Generally speaking, Tuesdays are designed to give players the day off while coaches game-plan for their next opponent and invite free agents for a work out. Sometimes the coaches are looking to immediately fill a vacancy on their roster but often they're just working out players to strengthen scouting reports; because teams never know when they'll need to fill a roster spot and this gives the team a more informed decision.
And sometimes you just find a better player than what's on your roster.
Case in point, when the team invited a host of defensive linemen on Tuesday, they were impressed enough with defensive end David King to sign him on their practice squad while releasing defensive end Kendrick Adams to make room.
In addition to signing King, the Bengals also worked out Kheeston Randall (former seventh-round pick by the Dolphins in 2012), David Carter (former sixth-round pick by the Cardinals in 2011), and Corey Irvin (third-round pick by the Panthers in 2009) all veteran defensive tackles.
Obviously this is in response to Devon Still's elbow injury that he suffered against the Detroit Lions.