Isn't that what one generally does when there is food by their mouths and they are hungry?
So, last night at dinner, I put some food on a spoon after she had begun eating (and thus was very hungry). Right when the spoon got to her mouth, she'd close her lips tight and try to take the food OFF of the spoon, with her fingers. This happened every time I tried it. Yet, she'd eat the food if I allowed her to take it off of the spoon, or if I let her hold the spoon.
It was totally cute. So, it would seem that not all kids open their mouths if you put food by them and they are hungry! Mine obviously has a preference for the delivery method.