Cannot Pass Gas
Think you may be thinking of rats not roaches.
Rats cannot vomit, so classes of rodentcides have been developed that amoung other things when ingested cause the rat to "vomit", but since it cannot, the rodent dies chokes on it's own vomit.
This method of rat/rodent control works well since humans, dogs and cats can vomit, thus the chances of a death by this method of poison is lowered.
On the down side, rats are VERY smart creatures. If they eat something that makes them sick, they will avoid it in the future. More over they will mark it with urine so other rats will avoid it as well. IIRC the term is called "bait shy", and it is the reason why chemicals are used that will allow a rat to consume a leathal dose in one feeding.
Squeek, squeek
Quote From Bugs Bunny:
"Look lady, I'm not a baby gorilla, I'm a rabbit. Technically known as rodentus rabbitus."
Launderess