It took time.
At first Kyle Cook was easing himself onto the field with a possession here or a series there. Eventually he split time (evenly too) with rookie center Trevor Robinson against the Cowboys and Eagles until Sunday, when Cook not only started, but participated during every offensive snap during Cincinnati's win over the Pittsburgh Steelers.
Pro Football Focus wasn't impressed, giving him a score of -5.3, the worst for a center in Week 16, writing:
It’s always hard reintroducing a guy into a line that was working well. This week at least it didn’t work for the Bengals.
Robinson, though impressive in his own right, playing well as a rookie, turned in his worst performance of his career against the Pittsburgh Steelers in Week Seven, though it was only his second career game and he replaced an injured Jeff Faine at the time.
However Cook wasn't the only one to struggle.
Kevin Zeitler also had a poor performance against the Pittsburgh Steelers with a PFF grade of -5.2 -- easily his worst of the year and first major negative score, notably the -4.4 run blocking. Clint Boling also turned in a -2.4 run blocking score.