Like a knowing smile, spotless windows attract the eye, reveal a rich inner life, and get hit by a lot of confused birds. Keep area avians addled with today’s Groupon: for $20, you get one hour of window-washing services from Reemtsma Window Washers (a $40 value). Reemtsma Window Washers services a 20-mile radius around Sioux Falls but may apply an additional charge to dusty portholes beyond that boundary.

Reemtsma has been bringing out glass’ natural invisibility since 2008, and the company services a conga line of residential and commercial clients. Washers efficiently apply suds to see-through surfaces and squeegee away nature’s nastiness, whether they find it on plate glass, stunt glass, or trompe l'oeil windows painted on walls to fool cartoon roadrunners. While the company normally fights dirt and yuckiness with the traditional tools of the window warrior, it also employs green cleaners on request for the same rate.