You have probably seen the cartoon where a bird is trying to swallow a
frog but the frog has a grip on the birds neck.  The caption is
usually 'Never give up' or  'Don't ever give up'.  I saw a sequel to
this cartoon which showed the frog sitting on the river bank with a
few bones at his feet picking feathers out of his mouth.  I can't
remember where I saw it but I would like to buy it or download it.

Is this it:
http://images.google.ca/images?q=give+up&hl=en&btnG=Search+Images

Here is a prior answer about the bird trying to eat the frog with lots
of links. Unfortunately, it doesn't have the cartoon with the reversal
that you're looking for.

http://answers.google.com/answers/threadview?id=523216
Q: Cartoon: Heron swallong a frog and a frong holding onto heron's throat

Not a cartoon but makes your point.

http://climbaz.com/temp/melissastuff/frog.html
http://climbaz.com/temp/melissastuff/FrogEatingBird.JPG
Photo ? bullfrog ambushes bird