Spot the popping dots

Furkle Stroy Williams found this unusual dice bobbing along in the river one day. He fished it out and spent some time observing the dice and trying to work out how it could be used.

“I’ve never seen a dice like this before,” said the Furkle. “It is squishy like the dice I buy in dollops, but the dots on this one pop in and out. I wonder why.” Where did the spot-popping dice come from? Did it float down the river from the Kingdom of Keys? Is it some sort of message from someone locked inside the kingdom?