That's because of the oil barrier. I like that idea, would like I'd thought of it!! Nonetheless, that's, I now 3D print cat food bowls which have an exceptionally modest, canted inward oil ring, which prevents kittie's fur from accidentaly finding oily. It works rather well and is not difficult https://angelobyqcn.isblog.net/the-2-minute-rule-for-pet-toys-53430977