A police uniform ought to make a frightened person feel that help has arrived. The Warwolves can use that expectation against people. One of the hunters hides behind that appearance during Excalibur's effort to recover Kitty, putting a predator in the middle of the response to its own pack's attack.
Kurt notices something wrong with the officer's expression. That is a much smaller clue than a silver creature charging down the tunnel, and it fits the kind of danger these enemies create. Once a Warwolf has taken someone's appearance, watching for claws and teeth isn't enough. The heroes have to pay attention to behavior as well.
Nightcrawler's investigation ends with him captured and carried back to the den. His agility and experience don't make him immune to being caught, especially when the enemy has already made the scene confusing. The disguise helps the hunter get close enough for the physical threat to matter.
Inside the den, the same creature offers Kurt to the Warwolf whose attempt to take Kitty's skin has gone wrong. A teammate's failure becomes a practical problem to solve, and another captive becomes the proposed solution. Their conversation has the casual quality of people sorting out a workplace inconvenience. Kurt's life barely enters into it.
The disguise also broadens the threat beyond the people Excalibur knows. Whoever supplied that appearance was a person before becoming something a Warwolf could put on. The story leaves the heroes dealing with both an immediate rescue and the evidence of people they couldn't save. Those borrowed faces make the pack's presence in London feel much bigger than the number of creatures involved.
A police uniform ought to make a frightened person feel that help has arrived. The Warwolves can use that expectation against people. One of the hunters hides behind that appear…
· Comics / Marvel / X-Men