に伏せる

lie face down on (a surface)

→ に
phrase Rare #25,117
lie face down on (a surface) に marks the surface someone lies on. In commands, 伏せろ means “get down!” or “lie down!”
JA: 銃声が聞こえたら、すぐに地面に伏せる。
EN: When I hear gunfire, I immediately lie face down on the ground.