https://www.youtube.com/watch?v=ewEQC98erC0
I do the first one on this video, stuff it with shredded paper and put the food in it. Nelly usually takes them to her bed and shreds them to bits.
Also I take a tube and fill it with three other tubes which are flattened and folded/rolled lenghtways, so you get loads of little tight spaces. Does that make sense? Stuff food down into these, in the middle, and they have to chew along to get to them. Nelly loves this. Sometimes I make three stuck together in a pyramid just for more of a challenge!