they both had to laugh, because they know that unknown, the monsters, the running is the best part. No chance is either of them going to give that up. No way they're just going to ignore whatever is going on here.
This is the one problem I have with Clara. They all had a certain relationship with the Doctor that was touching and sweet in different ways, but Clara and the Doctor really didn't have that definite chemistry because he sees her as more of a mystery than a person.