On Yom Kippur the kohein gadol (high priest) takes two goats and casts lots over them, with one becoming an offering on the altar and the other designated "for Azazel". (Azazel is a place in the wilderness where the other goat is sent.) The previous mishna described exactly how the lots were to be cast (drawn from a container, one in each hand). A mishna on today's daf explains that after this, he would bind a thread of crimson wool on the head of the one that is to be sent away and placed it at the gate, and also "the goat that was to be slaughtered at the place of slaughtering". This leads to a discussion in the g'mara: is this saying that he places the second goat at the place of slaughtering, or is it saying that the second goat also gets a strap that is placed around its neck -- the place where the slaughtering cut is made? The g'mara here concludes that it's the latter -- two goats, two straps that aren't the same in appearance. Why would that be? Because not only do we need to distinguish these two special goats from each other (for which marking one would be sufficient), but we must also distinguish them from any other goats that might be around as intended offerings. (Yoma 41b)

This reasoning demonstrates an important point: offerings require specific intent, so it's not enough to say "they're all going to the same place anyway". When offering each animal you need to know who or what, specifically, that animal is being brought for.