ULPT REQUEST: Box that opens and dumps its stuff out

I have a few people in my life who really need to be screwed with. I want to do something akin to mailing them liquified dog shit pours out on them when they open the box. I seem to recall The Anarchists Cookbook having something like this, but I don’t have a copy anymore. I could engineer something but I want to be sure it doesn’t open in transit. Or, any other good ideas? Unethical is great. I’m even ok with officially illegal, just not too illegal!