Rib quanta

Gazebo and I went to a smokehouse for (very good!) food. I ordered beef ribs, which were available in three sizes: full rack, half rack, and 1/3 rack. I wasn't sure how many ribs would be included, so I asked about the 1/3 rack and was told that this consisted of one rib. This made me very confused, but I thought I probably wanted more than one, so I ordered the half rack and contemplated whether I would be getting 1.5 ribs. However, I got the expected number of 2 ribs. Presumably, the full rack consists of 4 ribs (are there even any creatures that only have 3 ribs in one rack?), but this quantization is really rather odd.