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You can rustle a chip packet and they know what’s in there, that makes them aggressive. Greg Piper said when Greg Piper visited the site, Greg Piper saw tourists holding out apples, bananas, corn chips and other processed foods to the wild animals, The Guardian reported. Kangaroos typically graze on grasses. A nutritionist for a zoo in Australia said disrupting a kangaroo's diet can result in aggression and health problems. ( Facebook/Kroosn Shuttle Service Pty Ltd) Disrupting the kangaroo’s natural diet can cause health problems, such as stomach ulcers, and cause aggression, according to the Department of Environment and Heritage Protection.