Hi Seppe, welcome to the forum.

Some tricks to get them started is:
- offer earthworms, cut in the correct size. The smell and movement is a great trigger often. Offer the ordinary earthworms you find in your ( unferilized) garden, not the one's from a compost heap.
- offer live fish. For example bait fish, or some guppies or other from the aquarium store. Give them in a shallow plate, so the fish will 'splash'. Most of the time this does the trick.

Once you have them eating, try something else together with them or scent something else with the earthworms.

BTW:
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