1. Large toys (easily movable).
2. Effluvia, various orifices. Readily identifiable and cleanable. No problem.
3. Shredded paper (tissue, towels, extracted signatures of priceless books).
4. Small toys that multiply and move under your feet and onto stairs when your back is turned.
5. Cheerios and other foods that disappear into corners and sprout.
6. Meatballs and other solid food, mostly intact after landing and rolling under something else. These generally self-mummify and are no trouble until found weeks after the meal.
7. Non-shredded glossy ads from magazines. Acts as a frictionless surface (hilarious when encountered by the cat, less so when it’s your fundament on the floor).
8. Applesauce and other semi-solid (but still substantially throw-able) food, found much later after it has set and cured.
9. Toys, pointy-side-up, in the dark.
… and …
10. Sticky rice. Sticks to floor and socks tenaciously socks for weeks, utterly impossible to vacuum, forms a glue when you try to remove with towel.