Sorry, pacman's will eat anything and everything that moves in their tank, smaller, same size and bigger. They even try to eat your hand if you waggle it too close to them! If you place a larger frog in there thinking that the pacman can't possibly eat it, well it may not be able to, but it will sure try! This can cause impaction and probably the death of your critter.
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I think my frog owns a megaphone....