We were examining a deck of playing cards last week when I pointed out that the red things in the corners of certain cards were called, "hearts".
"Boom! Boom!", Island Boy stated.
"Huh?", thought I.
"Boom! Boom!", he told me again. Then, when I continued to look puzzled, he clarified by pointing to my tummy and saying:
"Heartbeat! Boom! Boom!"
Yes, Island Boy remembers listening to the heartbeat of his little sister while she was still inside of Mommy, so now whenever we see cards (or anything else) with a heart on it, "Boom! Boom!", is what we hear.