In one of the beginning sequences in the film, when Scott Turner is going to visit Amos Reed and Hooch gets loose, Hooch chases Scott down the walkway and tackles him. Scott was holding a muffin for hooch to distract him, and he drops it. We see a shot of the muffin rolling on the ground, and it lands upright. A few scenes later when Hooch picks up the muffin, it is laying on its side.
When Turner is on stakeout with Hooch, Turner is wearing glasses when he tastes the dog biscuit. When he feeds the biscuit to Hooch you can see his glasses on the dash. He then puts them on again in the next shot.
When Turner leaves Hooch in the car outside the police station and Hootch begins to "eat" the head rest, the foam insert is a white, cylindrical shaped piece of padding. When Turner returns to the car, you can see that the headrest has changed to a standard, yellowish foam commonly used in that make and model automobile.