I tried that. Even did gentle nudges with the arrow key to fine-tune the centering and rapid-tapped the space bar to be certain. No reaction from them whatsoever. Not from the one in the hall on the floor next to a locker, the one in the gym on top of the basketball backboard, nor the one under the ladder in the pool.
(To be certain, these are the envelopes with the heart-shaped seals, right?)