Katherine explains her tattoo:
From Cat’s Cradle by Kurt Vonnegut.
“Busy, busy, busy is what a Bokononist whispers ‘whenever [he] thinks about how complicated and unpredictable the machinery of life really is.'”
It is placed on the foot in reference to boko-maru.
“The boko-maru is a Bokononist ritual for ‘the mingling of awarenesses’. It consists in two people extending their legs, thrusting their arms behind them for support, and putting their bare feet together.”