One of our 747s hit a fox/something many years ago at high speed on a night T/O at Nairobi- nobody saw or heard anything unusual. When airborne, the F/E started putting the packs on and the aeroplane wouldn't pressurise. Caused a lot of head scratching. Eventually landed back for thorough inspection after dumping London fuel. The animal had obviously gone between the mainwheels and then been projected vertically upwards within the body landing gear bay at tremendous speed, smashed into the cabin floor and broken the pressure seal leaving a hole under the carpet. Nobody was sitting in that area so nobody was aware that there was a veritable gale blowing out through the floor! Not enough remains were recovered to identify culprit. A boar is pretty serious!