If someone has a surprise for you but won't tell you what it is, the best way to respond is to tell them you have a really great one for them too, and oh man, they'll never guess what it is but it's something they've always wanted. Eventually you'll agree to tell each other what your surprises for each other are, and after they tell you, you proclaim that their surprise is your cock in their ear. Works every time.

...except it was kind of awkward that one time with my grandma I guess.