Japanese bath tub lid is common item in Japanese home. The reason is that in Japan, family members share the same hot water (sounds dirty? Japanese wash their body outside of tub first, and bathing is thought as kind of lustral thing. And many Japanese take bath every day.) so this lid is used to keep the water warm for the next person when you are done.
Wow. Ok. So anyway, if you’re in Japan and someone starts snickering at you (besides for having a Japanese tattoo that that you thought meant “Great Power” and instead says “Lots Of Big”), it’s probably because you’re lifting the fancy lid off of your iPad 2 and they’re remind of all the times they bathed after their dad.