"If you allow yourself to fall into the vice of agreeing to [requests for just a few minutes of your time], they quickly snowball to the point where these parasites will use up 100 percent of your time — and squawk for more!"
ADDED: That quote — from Robert Heinlein (via Instapundit) — contains an atrocious mixed metaphor. First, time is analogized to money — "your total capital" — and then demands for it "snowball" — and here we've got an image not just of snow, but of getting larger and larger by rolling downhill. This increasingly large ball of snow somehow reaches a point where suddenly it's parasites — some sort of bacteria or fungi? — and they're consuming... well, I guess all that money. Having eaten all your money, these parasites "squawk for more" — they have powers of speech. What kind of parasites squawk? Maybe some animation in a TV commercial for an athlete's foot remedy. It's possible! But what happened to all the snow?
See, this is why I can't read science fiction.