what are some hints for gas formation? (beside gas bubbles)?

Answer 1

Jalapenos

Answer 2

While I'm not recommending that you try this (unless you know exactly what you're doing), but some gases like oxygen or hydrogen are flammable and in the presence of an ember (well, a burned but still glowing wooden stick, like you use to stir coffee) you can actually see the ember glow brighter on the formation of the flammable gas; a simpler way is to monitor pressure inside the reaction container (which I'm not going into, given diffusion from liquid considerations) but pressure change is an alternative. I guess the safest way would be to actually trap the gas using the proper set up (using liquid nitrogen which would work for oxygen gas, but ooooh, care is required as liquid oxygen is basically rocket fuel and is extremely and violently explosive)

Answer 3

Vinegar and some galvanized nails.

Answer 4

The stench.