Keeping a lot of state in your head
while modifying a program. "Don't bother me now, I'm juggling
eggs", means that an interrupt is likely to result in the
program's being scrambled. In the classic 1975 first-contact SF novel
"The Mote in God's Eye", by Larry Niven and Jerry Pournelle,
an alien describes a very difficult task by saying "We juggle
priceless eggs in variable gravity." See also hack mode
and on the gripping hand.