In the Back Garden challenge, you must collect thirty rabbits. Once you get to number 29, the last rabbit is in the compost bin. Get Wallace near the compost bin. Then, press L1 to have Gromit call him. He will blast the lid off, but only briefly. Gromit must stand on the trap next to it, and be ready to catch the rabbit mid-air.
Wallace And Gromit: Curse Of The Were-Rabbit