The very first Mishna in Massekhet Kiddushin taught that if marriage is to be carried out by an exchange of money (or an object of value), it must minimally be worth a peruta. The Mishna on our daf teaches that if a person hands a woman a date fruit and says, “Marry me with this date,” and then hands her a second date and, again, says, “Marry me with this date,” the marriage will take effect if either of the dates was worth a peruta. If neither one of them was worth a peruta – even if their combined value was a peruta – the kiddushin still does not work, since the husband’s statement separated each date from the other. On the other hand, if he said to her, “Marry me with this date and this one and this one,” we will add up the value of all three, since his statement appears to refer to the combined value of the dates. The Mishna continues that even in the second case, if she ate each one when she received it then we cannot view them as a single entity, and the marriage will only work if one of them was worth a full peruta.
The Gemara explains that in the last case kiddushin will only work if the last date is worth a peruta on its own. This is because we view each of the dates that the woman received and ate as loans, and a person cannot marry a woman on the basis of a loan. Given that the marriage will not take effect until the end of this process, it will only work if the date she is holding is worth a peruta, since the rest of the dates are no longer extant – thus they are simply money that she owes him, which cannot be used as kesef kiddushin.