Frodo stopped short in the act of spitting on the sidewalk when he saw Gandalf making Lotho suck up his (Lotho's) latest fresh gob of spit with a straw.
p.s. *This scene was actually witnessed by someone close to me in "real life."*
p.p.s. Yeah, it's quite disgusting I know - but look at Frodo's face! That just embodies the look of someone witnessing that scene! ^^^