I never said animals didn't
plan, and make decisions; I said they weren't
conscious. There's a big difference.
Planning is the evaluation of alternative, non-conflicting motor programs to determine the cumulative utility of a decision branch. (Basically, a decision-tree A* algorithm.) Animals do plan, but planning is not experienced consciously—it simply happens.
Human planning happens on this pre-conscious level as well. If you've ever been in a "flow state" where you felt like you didn't actually have to think about anything, because you just "reacted" the right way to every problem—that's planning. That's how it feels to be an animal.
Thinking is, as far as neurology has figured, the resolution of problems that occur during planning by the use of the neocortex to classify features of the current environment into schema, and re-trigger the planning process with expectation programs, looked up from those schema, substituted for motor programs. The most common form of thinking involves verbal expectation programs (basically, saying things to ourselves, in our heads, and then reprocessing those words as if they were external sensory inputs.) This is experienced as consciousness, and as far as we know, only humans do it.
Without the ability to think consciously—to resolve motor-program conflicts—an animal can't "argue" with itself about which course of action to choose. Instead, it just has a best intuition about which one will work out, and goes with it. These intuitions rely greatly on habituation—in fact, without expectation programs (and thus without semantic knowledge), memory as a whole consists purely of process knowledge—internal finite-state machines of habituated reactions.