var mammals = [
  {
    name: 'bantu',
    behaviour: [2,3,4]
  },
  {
    name: 'mantu',
    behaviour: [2,3,4]
  },
  {
    name: 'chantu',
    behaviour: [2,3,5]
  }
]

function getFilteredArray(mammals, searchString) {
  return mammals.filter(function(mammal) {
    return mammal.behaviour.indexOf(searchString) > -1 ? 1 : 0
  })
}

console.log(getFilteredArray(mammals, 5))