How Difficult Can It Be?

For the last few months, I've been looking for a third example of the kind of pun that goes

"It's only cranial medicine; it's not brain surgery."

"It's only interplanetary flight; it's not rocket science."

But to no avail. The closest I can get is along the lines of

"Litho-phlebotomy. It's like getting blood out of a stone."

But that doesn't seem to be in quite the same vein.

However, the complementary version of these puns, where things are easy, not difficult, seems to be more fruitful:

"Baking. It's a piece of cake."

"Outdoor exercise. It's a walk in the park."

"Juvenile recreation. It's child's play."

Even Mitchell and Webb only came up with the two examples above. But then, they are only a double act. If they'd had another collaborator, they might have come up with a third example for that sketch. Surely with their considerable talent... I mean, how difficult could it be? It's not exactly...