Final answer:
Slap gait is caused by weakness in the dorsiflexor muscles, leading to the foot slapping against the ground with each step, due to the inability to control the foot's motion properly.
Step-by-step explanation:
Slap gait occurs due to weakness of the dorsiflexor muscles which allows the foot to slap on the floor with each step. The dorsiflexor muscles are responsible for lifting the front part of the foot. Weakness in these muscles can lead to difficulty controlling the foot's motion, causing it to land with a slap as it contacts the ground. This condition typically lowers the sole of the foot to the ground forcefully, as can be seen when foot-tapping or jumping, and is essential in maintaining posture while walking.