Actually, the Foaming Frodo action figure was a running joke that both me and my husband came up with, and he decided
on his own to translate it into a cake for my birthday! He also chivalrously declared he would eat the portion covered with the 'foam,' as we had no actual vinegar in the house but had to use pickle juice! (thus the slightly yellow color that makes it look a bit worse in the photo!) He used so little that it didn't change the taste all that much, really, since most of it wiped off. Also having a rich chocolate cake and heavy cream cheese icing helped overwhelm any odd taste from the 'foam.'
The vinegar had to be added at performance time, but the baking soda was stuffed into the premade hole in the Frodo cake's mouth and when the two came together, it was quite theatrical, as the effect was much like Alka-Seltzer in water, creating a lot of CO2 very quickly! Perhaps this year, I should have a Mount Doom cake!
Cheers,
Lyta