Punisher, The Easter Egg - American History X Reference

During the mission at the zoo you can perform a special interrogation on the fountain. When you interrogate them you stomp their head against the fountain to scare and kill them. If you decide to execute the victim you should hear Castle say something like "What a shame, only a few feet from the curb," meaning that he could have stomped the enemies head on the curb (hence "Curb Stomp"). A Curb Stomp is the same execution used in "American History X". Happy Hunting!