1 {scene: Outside the Vatican City, at night. The Joneses and Dr Smith are partially concealed behind a barrier, watching the Swiss Guards.}
1 Ginny: The guards change shifts at midnight. That's our time.
1 Prof. Jones: Can't we just go to sleep?
2 Ginny: We may be on the verge of one of the greatest archaeological finds of the century!
3 Prof. Jones: Searching in a dusty old library? Give me fieldwork any day.
4 Monty: Seventy percent of all archaeology is done in the library, dad. I tell my students that all the time.
4 Prof. Jones: Don't be ridiculous!

This is probably funnier if you've seen Indiana Jones and The Last Crusade, as it references Indiana Jones' line that "Seventy percent of all archaeology is done in the library."

If you haven't seen it, I won't spoil why that line is amusing in the film.

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2017-03-19 Rerun commentary: Honestly, I wonder about the accuracy of that 70% figure. I suspect that in reality it may actually be higher, and that substantially less than 30% of the work is done in the field.

I haven't formally studied archaeology, but I know from experience with astronomy that you're lucky if more than about 1% of the work in astronomy is done in an observatory.

Oh, and yes, that barrier that just happens to be sitting there in St Mark's Square does seem to be conveniently handy for them to hide behind, doesn't it?