Prepare cake mixes and bake according to box directions (any size pan). Prepare pudding, chill until ready to assemble. Crumble sandwich cookies in small batches in food processor, scraping often.
Set aside all but 1/4 cup.
To the 1/4 cup of crumbs, add a few drops of green food coloring and mix using fork or shake in a jar.
When cakes are cooled to room temp, crumble into a large bowl.
Toss with half the remaining cookie crumbs and chilled pudding.
You probably won't need all the pudding, mix the cake and "feel" it, you don't want it soggy, just moist; ge ntly combine. Line litter box.
Put mixture into box.
Put 3 unwrapped tootsie rolls in microwave safe dish and heat until softened.
Shape ends so they are no longer blunt, curving slightly.
Repeat with 3 more tootsie rolls and bury in cake mixture. Sprinkle the other half of cookie crumbs over top.
Scatter green crumbles lightly over top (chlorophyll in cat litter). Heat 3 tootsie rolls in microwave until almost melted.
Scrape them on top of the cake and sprinkle with cookie crumbs.
Spread remaining tootsie rolls over top; take one and heat until pliable, hang over side of litter box, sprinkle with cookie crumbs.
