I'll sometimes take their crumble and wet it, so it's like a mushy glob of dough. I do this because the 'crumbles' are really terrible, it's more like the dust and crap from the assembly line they swept into a bag and sold it to you. Even when I get the 'whole' pellets, half of them are busted up or dust in the bottom of the bags.
I really hate wasting all this that I paid good money for ! So I'll pour water on it and make it into a thick glob you can squeeze. This way they eat it ALL, the dust does not just get walked and ground into the mud and lost. IT's also softer, smooshier, so the whole gizzard thing, there's nothing to grind up really, so the oyster shells, are more for nutritional value really. I'll also sprinkle ground oyster shells on top of the wet food every day too, and let them pick what they want/need to eat and so far, everyone seems happy and I am wasting a lot less food.
Aaron