We originally bought one for DS at the giftshop at Kew Gardens...
It's a ball-shaped thing, around the size of a tennis ball. Basically it's a balloonish thing filled with goo and wrapped in a net like a string bag or orange bag. When you squeeze it you get bubbles of goo-filled balloon popping out through the gaps in the bag, and because the balloon is stretched thinner over those bits the colour of the goo shows through. There were two colourways available, blue with snot-green goo and purple with bright pink goo.
Now DH has trodden on it (grrr) and it's sprung a leak. It's DS's favourite thing at the moment so I'd like to get a replacement, but I'm not likely to be back at Kew any time soon and I don't know what it's called or where I can get one (and you should just see the sites that come up if you Google gross goo ...).
Anyone recognise my admittedly lame description?