snap to (attention)
1. To suddenly or abruptly begin paying attention. I was lost in a daydream, but I snapped to when the teacher called my name. The kids snapped to attention when I slammed the ladle down on the kitchen table.
2. To quickly assume military attention. You become trained to snap to attention when a superior officer enters the room.
snap to (attention)
in. to come to attention; to look alert immediately. When they realized what was happening, they began to snap to.