It appears as if Leonard and Howard are working on a very important project and they are rather excited over the possibility of completing something together. In fact, they are even talking about the last time that they actually created something with each other, outside of the Lego Millennium falcon that they created last week in Howard’s apartment.
While they are working on the project, Bernadette and Penny show up and offer to help them in any way that they can. Before the have the opportunity to back out of it, Leonard suggests that they could be able to help, and Penny reluctantly makes good on her offer. In fact, she even jokes about the possibility that she could come up with a scientific breakthrough before Leonard!
We have watched the relationship grow between Leonard and Penny over the past several seasons and it is always rather interesting to see the changes take place. This is just another one of those changes, and it will be interesting to see where it goes from here.