From Creatures Wikia
Injecting any one of the 3 Goop Vendors produces a vendor. A symbol on the button tells you which type of goop will be vended: the word "Food" on the dispensor means that particular vendor dispenses Goop loaded with Food, for example. All Goop objects vended, as long as they are not modified while they are laying on the ground, can be stacked. There are interesting Bugs with the Vendor: you can make Goop float in midair if you click the button 4 times, although placing any stackable agent on top of it results in the Goop falling to the ground. Using an Agent Modifier to make the Vendors stay at the top of the screen works until you pick it up with the hand. However, modifying it to stick to the screen works no matter how many times you "pick" it up.