I'm sorry, but that isn't how science works. We'd need to verify that there are no manx genes in the line of your cats (a manx is a feline breed that sometimes doesn't have a tail, but can interbreed with common cats and sometimes the recessive lack of a tail comes through, this is typical genome variation, not evolution). We'd need to verify through repeated experimentation that this would occur in other felines (that it is reproducable). The lack of tails can be explained through a recessive variation in the existing genome, not as evolution of the genome.
I have no doubt that your aunt has cats without tails. I do doubt that they are being born that way because of an evolutionary change caused by her cropping the tails of their ancestors. Without something better as a source, you're simply not going to sell any scientist on this (sorry).

Well, you did just attempt to present your aunt's cats as evidence of your point which doesn't fullfill the criteria. Many people don't know what a falsifiability means or what a falsifiable hypothesis is, and I wasn't sure if you did or not.

-- Jeff

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"Government is not the solution to our problem, government is the problem." --Ronald Reagan