kick inとは？

反射的か自動的に反応するすることです。

2:38 their training just kicked in.（日頃のトレーニングが発揮された）

0:42にもあります。

http://www.youtube.com/watch?v=byqT_LQFARA 0:18 backup system should've kicked in

http://www.youtube.com/watch?v=_8RSjz4Cz0s  2:07 her body's memory kicks in
http://www.youtube.com/watch?v=HOUDa6dqHf0  1:21 the adrenaline kicked in
http://www.youtube.com/watch?v=kVQsYDKaDkU&feature=g-vrec 0:56 When I looked over my shoulder and saw the bull I was obviously getting more scared as they were approaching, but at the same time, the adrenaline in me was kicking in.

練習問題解答
a-2372 kicked in
b-3832 kick in