...because both are often talked about in the Reality Checkpoint . -- MoonShadowAll good entries, but Rachael takes it.
...because both resemble wellies . -- Rachael
...because both are required for backpacking around Llanfairpwllgwyngyllgogerychwyrndrobwyll-Llantysiliogogogoch . -- Steve
...because both can be used to guide Santa's sleigh . -- MikeJeggo