Kiddushin Chapter 1, Mishnah 4. This mishnah deals with the way various types of animals are acquired, and with the question of which acts of acquisition are effective for each of them.
"Behemah gassah nikneis bimesirah":
A large animal - such as cows and oxen - is acquired through mesirah (handing over). Mesirah means that the original owner hands the buyer the reins or something else attached to the animal. The animal need not move from its place: the very act of the buyer taking hold of the reins symbolizes the transfer of ownership.
The reason for this: lifting a large animal is difficult, and even pulling it is no simple matter, since it does not move easily. The Sages therefore ruled that mesirah is sufficient.
"V'hadakah b'hagbahah" - the small animal and the dispute among the Tanna'im:
Rabbi Meir and Rabbi Elazar: Small animals - sheep and goats - are acquired through hagbahah (lifting). Since people normally pick them up, the appropriate act of acquisition for them is lifting, and the rule is that anything normally lifted is acquired specifically through lifting, and not through pulling or handing over.
"V'chachamim omrim: behemah dakah nikneis bimshichah" - in their view a small animal is acquired through meshichah (pulling) as well, because at times it digs its hooves into the ground and lifting it becomes difficult. They therefore were lenient and ruled that it can also be acquired through pulling.
The halachah is that both a large animal and a small animal are acquired through pulling, and of course through lifting as well for one who wishes to acquire them in that manner.
In summary: In this mishnah we learned the ways animals are acquired: a large animal is acquired through mesirah, because it is difficult both to lift and to pull; a small animal is acquired through hagbahah according to Rabbi Meir and Rabbi Elazar, and according to the Sages through meshichah as well, because at times it digs its hooves into the ground. And the halachah is that both are acquired through pulling, and certainly through lifting.