Lion IRC:
Apparently Adam and Eve were clothed in animal skins involving the slaughter of an animal/s.
Just had a quick look at discussions on one or two Christian sites about this and its interesting although not surprising there'd be people asking all types of questions (its a new one for me). There is no mention of animals killed but there are quite a few interesting ideas.
Obvious one is : God created man therefore a skin of sorts can also be created for clothing , or the wool of sheep and similar animals were used . Another suggestion: Adam and Eve commited sins and God gave the first sacrifice of animals for their sins and used the skins of the sacrificed animals and there is also the garments of light translation from some texts, in which I would need to read more on (if only I had the time). Quite a few theories on this particular verse.