Phone
If the hidden file room is so far beneath the building, how is it Cooper has cell service?
shareThere are amplifiers/relays for cellphones, just as there are for WiFi - we have a really old-fashioned basement at my place of work (thick concrete walls with steel reinforcement), and we had to install a few of them to get cell coverage for our employee's phones.
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Kung-Fu movies are like porn. 1-on-1 first, then 2-on-1, and then a group scene...