Although these two terms sound similar they are actually very different things and therefore should not be used interchangeably.
An anal eater is someone who expresses some kind of anal-compulsive behavior in their eating habits. What exactly that means is highly subjective and may only be considered as such in the eyes of the person calling them an anal eater. Examples of eating habits that may be seen as 'anal' range from vegetarianism to someone who won't allow any of the different foods on their plate to touch eachother. I once called my mother an anal eater because she refuses to serve common condiments such as cream cheese, salad dressing or even barbeque sauce in their store containers when company is over for dinner. Instead, she empties the contents into some nice porcelain bowl so as not to give a 'tacky' look to the table, only to transport the unused portions back into their original packages which she stashes in a cabinet until the meal is over.

On the other hand, an anus eater is someone who engages in very thorough oral sex practices. Rather than sticking strictly to the genitals of their partner, they go all out (or should I say in?) It is also something I would never call my mother.

An anal eater is ... well ... some person (or biological entity) which uses its anus to eat. Planaria are anal eaters, for in planaria, the mouth is also the anus. I don't think most human beings have mastered this trick yet, but if emergency room records are any clue, there are plenty of resourceful individuals striving to make headway in this difficult field. (So, Mr. Smith...tell me again how you managed to get a kumquat stuck in there?) (It was one in a million, Doc! One in a million!)

An anus eater is, quite clearly, some person (or biological entity) which uses its mouth (or anus, or other gastroenterological part) with which to eat anuses. Or even a single anus. It should be obvious to everyone that anyone who eats hot dogs or sausages or cat food (or probably hosts of other delicious foods rich in bi-products) is an anus eater. Also, in all likelihood, a lip, feather, and beak eater. (Awww...you can really taste the anus...)

It would be interesting to see how much overlap there is between these two groups. I'm guessing probably quite a bit, as it seems to me that any anal eater worth his or her salt is going to be drawn to the prospect of sausages or hot dogs sooner, rather than later, in their anal-ingestive career.

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