Only if the spine doesn't get stuck in their throat.
No.
Well... I personally think that cactus finches eat cactuses because in some images on the web, if you type in cactus finches, some will have a picture of a cactus finch eating bits of a cactus.
Cats may eat cactus due to curiosity or boredom, but it can be harmful to their health. To prevent this behavior, keep cacti out of reach and provide alternative toys or activities to keep your cat entertained. If the behavior persists, consult with a veterinarian for further advice.
Eating, wearing, drinking
yes! eating the nip of pencil is harmful if its made up of graphite
NO.
no
yes I believe it is harmful
No, eating eggs in not harmful. Though, eating raw eggs could make you sick, but otherwise any form of egg isn't harmful if it doesn't have a disease like salmonella in it.
Eating, wearing, drinking
Phosphorus.
No it is not harmful but it is likely that they will not enjoy eating it.