When I did this project in 1st Year Drawing, we did it under the general name of "Transformation Drawings", but I think it applies to what you're doing. We had an American eagle ~decomposing~ into a Swastica in 6 stages, or flower turning into a house in 4...something like that.
For myself, i drew someone ripping his chest open, and the small intestines and skeletons ~became~ the white stripes of those fictatious prison clothes, with the arteries and large intestines becoming the black stripes, and the heart becoming a plaque with the name of the crime. This ~decomposition~ was drawn ~cartoon-style~ in 6 stages, that is one separate drawing per ~frame~, with a total of 6 frames, with the frames in the middle being the ~synthesis~ of a set of entrails+prison clothing. Give me your e-mail if you want to see a thumb of my project (i hope i still have it)
If you want a nice effect with single or double replacement (esp~ double replacement), you'll want things that are vastly different from each other for a dramatic effect. Your chicken + water is a good example, because a pile of liquid looks nothing like a chicken, yet if you were able to make a smooth transition, or a transformation, that relates the two, it would look quite spectacular. However, if you're doing this for an art class, try not to do something so cliche. I actually love cliches, but I know for a fact that non-cliches score higher marks. Anyway, so with you chicken soup, for a smooth transition, I imagine that you can either draw both the chicken and water SEPARATELY turning into a single chicken soup (3+3+1 frames), or JUST the chicken turning into water, which then turns into chicken soup (4+4 frames), or both the chicken and water TOGETHER turning into chicken soup (4-6 frames).
Other ideas:
oil barrels + 747airplanes = Iraq flag
a woman + a black veil = election booth
dinosaur bones + crucifix and its beads both decompose into famous words of knowledge in a book
a butterfly => a beautiful painting <= a nebula
musical insruments => paint strokes; art supplies => music notes
a semi-trailer ~assembling~ into a giant robot...
(and so forth...) Try to mix some profound themes in there. Hope that helped; thanks for reading
