Emulsion, osmosis or brownian motion?

We had antelope for dinner at the local South African restaurant; eland is mid-way between veal and steak and as promised very tender and the kudu was very tasty too. Crocodile tail on skewers was tasy for a starter, milk tart was very Portugese for dessert and with the bill came two shot glasses of creme de menthe and amarula. I'm not going to attempt to explain sbisson downing it like a tequila shot, but I do wonder about the physics and chemistry of the alcohols. I was sipping it slowly but we ended up watching my drink more than finishing it. The amarula is the top layer and it floats on the creme de menthe, but every now and then a hole would appear in the layer and move around as creme de menthe gushed up to the top; after a while the hole would close and the creme de menthe would stabilise. I'd take another sip, another hole would open up and off went the gusher again. Many minutes of entertainment and speculation. Must see if I can get the same effect with something less urgh-that's-sweet than creme de menthe...