LOS ANGELES (KABC) -- Los Angeles police are investigating a bizarre case of trespassing that involves a man slapping a hippo's butt at the L.A. Zoo.A video surfacing on social media shows a man hopping over a barrier, reaching down and quickly slapping one of two hippos' behinds. He then quickly gets out and appears to give a thumbs up as he flees.It's unclear when the incident happened, but officials said it was a big risk because hippos kill more people than lions in Africa.The two hippos, mother Rosie and daughter Mara, were the ones in the enclosure. Zoo staff also said it was a potentially dangerous incident not just for the man, but the mom and daughter hippo.