Most modern houses in Australia are built on concrete slabs. They are vented at the floor & ceiling of each floor level to allow good ventilation of the wall cavity and also aids the damp course barrier. This ground vents if not screened invites reptiles, rodents & pest to take up residents in the wall cavity of your home. In this picture you can see an Australian Eastern Brown Snake has happily taken up the offer and shifted in. Netting has been placed over one of the vents and the others taped up , in a bid to force the reptile out and into the trap so it can be relocated to a safer location away from human contact.