Coffin Gas Tank Is There Any Kind Of Poison That Would Make A Lot Of Gas Emanate From A Dead Body?

Is there any kind of poison that would make a lot of gas emanate from a dead body? - coffin gas tank

There is speculation, my family that my great-grandfather was poisoned. This is due to the accounts of some people at his funeral, and claimed that his body expired gases while the coffin broken by pressure. Depending on whom one asks, say some, it was open. Is there some kind of poison that can happen?