I have read of Deer mice and think they would be a good possibility. Agreed... the gooey stuff in the middle sparks their interest but the overall size intimidates these guys at any age. I see it here with all of my animals to some degree, more so with certain individuals so the halved pink approach is on the right track with the babies. I also feel that the bulk of the item is important, not just length and a day old Deer mouse pink would meet both criteria... shorter in length and not as big around. I also think they accept compromises between length and bulk, I watch all of them eat... babies through adult... and most of them thouroughly investigate the item, obviously considering length and bulk at the same time. They seem to be able to compromise and accept a longer item that is slimmer, or a bulky item that is much shorter in length, but naturally the bulk can't bee too large no matter the length. If it is too long and bulky, they shy away. I would venture to guess that if we had a good supply of these tiny Deer mouse pinks, most smaller babies would take brained f/t fairly quickly.
Mike