As Samantha was kissing David she lost her control as she liked the feel she was getting. As she was kissing him she wanted to get a better position so she started to move so she was now straddling him and the chair,
What Sam did not know was that she had not distracted David like she thought, so as she was adjusting her position David had enough time to hit the enter key on the computer which started the change that he had started imputing before she tried to distract him.
So as Samantha sat back down on David's lap she started getting turned on even more than before, son much so that she did not notice her breasts getting a little bigger. All she could think of was that she needed something inside her.
As Samantha continued to kiss David her hand went to his belt to start undoing it.