Bullfrog tadpoles are large and brown/gray, leapards change into frogs when very small.
This reminds me of my buddy Boudreaux:

Boudreaux been fish'n down by de bayou all day and he done run outa night
crawler baits. He be bout reddy to leave when he seen a snake wif a big frog
in his mouf. He knowed dat dem big bass fish like dem frogs, so he decided
to steal dat froggie. Dat snake, he be a cotton mouf water moccasin, so he
had to be real careful or he'd git bit. He snuk up behin' dat snake and
grabbed him roun de haid. Dat ole snake din't lak dat one bit. He squirmed
and wrap hisself roun' Boudreaux's arm try'n to git hisself free. But
Boudreaux, he had a real good grip on de snake's haid, yeh. Well, Boudreaux
pried his mouf open and got de frog and puts it in his bait can. Now,
Boudreaux knows dat he cain't let go dat snake or he's gonna bite him good,
but he had a plan. He reach into de back pocket of his bibs and pulls out a
pint a moonshine likker.
He pour some drops into de snake's mouf. Well, dat snake's eyeballs kinda
roll back in his haid and his body go limp. Wit dat, Boudreaux toss dat
snake into de bayou. Den he goes back to fishin'. !
A while later Boudreaux dun feel sumpin' tappin' on his barefoot toe.
He slowly look down and dare wuz dat water moccasin wif two more
frogs........