What did Jesus tell Nicodemus that confused and perplexed Nicodemus?

Jesus told Nicodemus that one had to be born again in order to enter the kingdom of God.

What questions did Nicodemus ask that let us know that Jesus' statements confused and perplexed Nicodemus?

Nicodemus said, "How can a man be born when he is old? He cannot enter a second time into his mother's womb and be born, can he?"