The technical term for this ia a minced oath, and you may be able to look up a list. The difficulty is that, like other oaths, they are more used in speech than in writing, and, being non-standard, they vary from place to place and among age-groups. But I have heard what the deuce, what the flip, what the hey, and even what the blank, as well as the more usual what the heck and what on earth.

The technical term for this ia a minced oath, and you may be able to look up a list. The difficulty is that, like other oaths, they are more used in speech than in writing, and, being non-standard, they vary from place to place and among age-groups. But I have heard what the deuce, what the flip, what the hey, and even what the blank, as well as the more usual what the heck and what on earth.

There is, of course, a rather more subtle point: while 'What on earth are you doing here?' just shows greater surprise than 'What are you doing here?', 'What the hell are you doing here?' is not a straightforward question; it shows anger, at least. This may be one of the few places where bad language is actually necessary (to convey the full meaning).