Thanks for the response!
Mainly just more animations rather than the one static face if possible!
Like either of them fanning away the gas with their hands or tails due to the smell, or more facial animations of them being relieved or possibly even smug by their own gas.
As for foods it could really be anything that would cause a lot of gas/bloating. They could also affect the color of the gas (green, yellow, brown) and the sounds produced (aka, bigger bassier farts, or loud wet ones)