Turn you into a toad

old wives tale, never researched it, though Murfies probably right.

other things, like flying on broomsticks, that comes from an old traditions where you would jump over the besom [broom] it looked to some as though we were trying to ride the broom and it kind of escalated. black animals, simple, black equals evil so a black animal must be a witch in disguise. cats in general were seen as evil since they were night creatures, and rather solitary. they were banned for a little while in Europe, caused a plague because no one was keeping the rat population down. also, the reason witches were usually thrown in water was it was believed water was pure, a pure soul sinks while an unpure witch floats. so you either drowned or you floated, were retrieved, and killed. [little off topic, but in case you were wondering about other tall tales about witches]

Thanks guys all I wanted to know was where the myth comes from, I know it isn't possible, sadly hahaha

Why are certain animals portrayed in witchcraft? Is it because witches kept them as familiar and/or could shape-shift into them at will?

as i said before, black animals, like cats and dogs, were believed to be evil, and be aligned with the devil. same went for any nocturnal creature, bats, and undesirable creatures, toads, snakes so forth. some people who were pegged at witches [some were but most weren't] typically lived alone, sometimes in the woods or the outskirts of town, with a lot of these animals around. because they liked them, or because they knew each creature could keep them safe and healthy. either way, people would begin to talk and make up stories, how they 'saw the old lady talking with the cat, then the mayor got sick and the thatcher saw the cat hanging around the mayors house'. while any logical person could come up with the cat was hunting mice, back then, people would believe the 'old lady' was telling the cat [her familiar] to go and poison the 'mayor'. that's how these things start. people get scared and come up with stories to calm themselves. still happens today.

As has been mentioned, the idea that Witches or other magic users can turn someone into a beast has ancient roots. Another example is the Sorceress, Circe, who turned Ulysses men into swine. I suspect these myths carried forward into medieval times and the stories persisted. And of course we don't know whether or not some Witch might not have sought to cause her neighbors to fear her and leave her alone by threatening to turn them into something unpleasant.