Cows and catapults.

[Spino]

Why should they launch perfectly edible and healthy food?

Most of the time the stuff they launched was neither edible or healthy. More often than not they used the bodies of dead animals whose carcasses were already be in a state of decay. This would guarantee that a whole host of vermin had taken hold in the carcass and would be scattered all over the place when the body impacted on the ground or a building. Even if the body was recently killed the explosion upon impact would be sufficient to scatter the pieces wide and far enough to attract an unusually large number and assortment of vermin to the scene, thus increasing the likelihood that an outbreak of disease would occur.

[TheImp]

"Another Mongol tactic was to use catapults to launch corpses of plague victims into besieged cities. The disease-carrying fleas from the person's body would then infest the city, and the plague would spread allowing the city to be easily captured, although this transmission mechanism was not known at the time."
Taken from: http://en.wikipedia.org/wiki/Siege

Surely, in middle-age era, people knew some ways to have great fun!

[alpaca]

Most of the time the stuff they launched was neither edible or healthy. More often than not they used the bodies of dead animals whose carcasses were already be in a state of decay. This would guarantee that a whole host of vermin had taken hold in the carcass and would be scattered all over the place when the body impacted on the ground or a building. Even if the body was recently killed the explosion upon impact would be sufficient to scatter the pieces wide and far enough to attract an unusually large number and assortment of vermin to the scene, thus increasing the likelihood that an outbreak of disease would occur.

Ah yes, irony is so hard to spot over the net

[Spino]

Ah yes, irony is so hard to spot over the net

Hah! It is when you're trying to read through a thread while trying to get work done!