A more thorough explanation:

Spondesne? Spondeo (spon-deez spon-dee-oh) is a Latin phrase used in Roman law. It refers to a specific agreement between two citizens. The phrase means "Do you agree to undertake?" and "I undertake" respectively. This phrase was used to create a sponsio, which was a type of legal obligation.

For example, if two Roman citizens were making a legal agreement, one might ask the other, "Spondesne?" The other would respond, "Spondeo." This exchange would create a sponsio, which was a legally binding agreement.

Another example might be if a Roman citizen was making a promise to pay a debt. They might say, "Spondesne me centum nummis?" (Do you agree to undertake that I will pay 100 coins?) The other person would respond, "Spondeo." This exchange would create a sponsio, which would legally obligate the debtor to pay the debt.

The phrase "Spondesne? Spondeo" was a specific legal phrase used in Roman law to create a sponsio. A sponsio was a type of legal obligation that was only available to Roman citizens. The exchange of this phrase between two citizens created a legally binding agreement. The examples illustrate how this phrase was used in different legal contexts to create a sponsio.