Bava Batra 53 - Is the Presence of the Giver Required?
After a price has been agreed upon, some indication of the seller's readiness to transfer property is necessary. This can be accomplished by the seller instructing the buyer to go and perform an act of chazakah upon the land. But where the seller is present, he does not have to say anything, and his silence alone indicates his acquiescence.
What is the rule for a gift?
Rav says that the giver gives the gift generously, out of fondness for recipient, so no further instruction is necessary, and the chazakah can be performed in his absence. Shmuel says that since the giver receives no money, certainly his instruction is required. Actually, Shmuel agrees that the gift is given generously. However, here possibly no gift is being given at all.