If they're not cleaned every few days, windows turn black and begin emitting a high-pitched scream that makes dogs pregnant. Prevent a neighborhood outbreak of puppies with today's Groupon: for $40, you get $80 worth of residential window-cleaning services from Clearer Image Window Cleaning. This Groupon is valid within 25 miles of midtown Memphis.

A locally owned company with more than 15 years of experience, Clearer Image makes pane polishing virtually painless. Dial up a friendly scheduler and pick a date and time for the service, noting which windows need cleaning ($8–$13 each) and how many T-shirt cannons shooting eggs have fired at your house since the last scrub.

Soon, a team of window wizards arrives with cleaning potions and squeegee wands, levitating level by level to spritz rooftop jalousies and tree-house skylights. Streaks, spots, and bug graffiti vanish in a jiffy, revealing thoroughly clean, subtly sparkling glass. Though today’s Groupon doesn’t apply to the panes of corporate skyscrapers, it may be used on tiny houseboat portholes and the walls of human aquariums.