cow... actually you use the gases from decomposing manure.
5 is how many it takes to make a balloon octopus
they make sound by using their mouth and diaphragm and they use it for scaring off prey, defending territory, mating and communicating.
helium's density is lower than that of air (which is 79% Nitrogen, 20% Oxygen), do it floats like a piece of wood in water.
Wow. What an interesting project idea! I think the broad categories are: They are used as work-mates [teams of oxen pulling plows, etc; horses used by drovers, mounted police, etc]; they are used for...