Yes, try a little chocolate on the traps but it will probably be more effective to use a little slice of Mars bar or Milky Way etc so that the soft centre can be squashed onto the trip flap. Otherwise. mice can deftly lift a piece of bait right off the trap.Also, they eat more confidently with some overhead cover, so construct a little card 'tunnel' (say from a cornflakes box) about 3" high to place over the trap. I've had mice issues in my veg bed before and killed up to a dozen with two traps over the space of a week until the problem ended.