Does anybody know what glue is made of (horses hooves really)? Why there are so many different types of glue, why thinner glues are stronger than thick glues, and why they can be so smelly? And while we’er at it, are violin strings really made out of cat guts?
Some glues are made with animal products. I can’t remember which kinds at the moment though.
There are different kinds of glue for different applications. For example, model cement dissolves plastic and causes it to stick together when it dried.
I think they smell because some of the glue’s ingredients evaporate during the drying process.
Just guessing here, but a thinner glue probably gets down into the pores of the material better than thick glue, resulting in a tighter bond.
Not sure about the cats’ guts, but they had to use something before there was nylon! 
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According to this site cat gut is really sheep gut. http://www.suru.com/surucor.htm
Animal glue, typically made from hides, is not very common aside from antique restoration and some furniture building. It comes in granular form and has to be mixed with water and heated to be used. It spoils quickly so I don’t think there is any ready to use liquid form of it. The main advantage is that it doesn’t set quickly which is good for things that take some time to assemble. It is absolutely not waterproof or even moisture resistant which can be an advantage, old hide glue can be removed with warm water or steam.
Vous means
It’s called “casein” and was years ago in much the same way that PVA glue is used today.
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