Whilst purusing some sell sheets this evening, I came across the following for Topps' upcoming Spongebob Squarepants set:
Yes, that "card" turns into a sponge when put in water. My daughter is only now getting into Spongebob. I may have to make this the first card product that we break together.
The sponges look like they're an insert. There's also other fun stuff like letter stickers but I might get to that at a later date. I just couldn't hold off on my excitement for sponges.