Acts 5:7-10 (NIV):
"About three hours later his wife came in, not knowing what had happened.
Peter asked her, “Tell me, is this the price you and Ananias got for the land?” “Yes,” she said, “that is the price.”
Peter said to her, “How could you conspire to test the Spirit of the Lord? Listen! The feet of the men who buried your husband are at the door, and they will carry you out also.”
At that moment she fell down at his feet and died."
In this passage above, we see that before pronouncing Sapphira's sin of telling a lie, Peter did a kind of test by asking her for how much she and her husband had sold the land. It was only after she stated that the sum of money laid at the apostle's feet was exactly the sum of money she and her husband had acquired (which was not true) that Peter declared her act of lying.
However, we don't read in the verses earlier that her husband Ananias had also been given such a test:
Now a man named Ananias, together with his wife Sapphira, also sold a piece of property.
With his wife’s full knowledge he kept back part of the money for himself, but brought the rest and put it at the apostles’ feet.
Then Peter said, “Ananias, how is it that Satan has so filled your heart that you have lied to the Holy Spirit and have kept for yourself some of the money you received for the land?
Didn’t it belong to you before it was sold? And after it was sold, wasn’t the money at your disposal? What made you think of doing such a thing? You have not lied just to human beings but to God!
When Ananias heard this, he fell down and died..” (Acts 5:1-5)
We don't have even a single word spoken by Ananias. If so, then how was it a lie? After all, Ananias could have said something like, "But I never said I brought ALL the money that I received, so I didn't lie."
One may say that that was an act of lying to the Holy Spirit, but then it is not clear why Ananius' wife, unlike her husband, was still "given a chance" later to lie, that is, before her sin of lying could be pronounced by Peter. Actually, I wonder what would have happened to her if she had said the truth instead, that is, something like "No, this is not the whole sum. We decided to put aside some for some other needs."
Unless the act of putting money at the apostles' feet explicitly meant putting ALL the money that you had (like in the previous chapter we read: "All the believers were one in heart and mind. NO ONE CLAIMED THAT ANY of their possessions was their own, but they shared EVERYTHING THEY HAD." Acts 4:32) I can't find any explanation to that.
And even then, though, I still don't get it when then Sapphira didn't die right away like her husband, but was given a chance to be exposed in her lies first.