Meaning: something of great (exaggerated) weight or size. Use examples.
Rewrite 1: the 500-pound canary
Rewrite 2: the 6-ton birthday cake
Rewrite 3: the eight-story bungalow
Rewrite 4: a gorilla with enough muscle to lift a tree house

Comment: I can’t resist telling a couple of jokes here: What does a 500-pound canary say? “Here kitty-kitty…” Where does an 800-pound cat sleep? Anywhere he wants to. What don’t you tell a centipede to hurry it up? Shake a leg. (You’d want it to shake all of its legs.) You can have a lot of fun with this one, and I encourage you to do so.

Note: "800-pound" (and similar constructions) is often written out as "eight-hundred pound."

More reading about clichés
What I found when I googled “clichés”:
• CISAB Animal Proverbs and Cliches: Animal Proverbs and Clichés from the Center for the Integrative Study of Animal Behavior, Indiana University, USA.