Whenever cats are behaving abnormally, you know that something is up. It is either physical or emotional. Anything ranges from having a new member in the family, changing laundry detergent, dirty litter box, fleas or having urinary track infection could cause change of behavior.
Normally cats don't act strange because they are mad at you. Most of time, it could be an indication that they are stressed over certain things or they are having some health issues, such as lack of certain mineral that they need.
I came across a great page of information that shares a story of a cat that eats her own litter, and explains the possible cause of her anomaly.
There is a condition called pica that is caused by a deficiency in the diet. Your cat is possibly trying to get minerals that she's not getting enough of from her food (or an illness has made her deficient in a mineral, such as iron)
Fleas can spread parasites (such as tapeworm), and parasites may cause anemia. I've read where some flea infestations can be bad enough to cause significant blood loss just from the biting alone. Also, some cats are highly sensitive to fleas, and they can cause a lot of stress. - Kurt
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