床に伏せろ！
Words
床
(とこ)
bed; bedding; sickbed; alcove; riverbed; seedbed; straw "core" of a tatami mat; floor
に
(に)
at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although
伏せる
(ふせる)
to lay something upside down; to turn something over; to lay something face down; to cover; to lay (pipes); to lay (an ambush); to hide; to conceal