(Not So) Solid Evidence

A soldier was given the job of hunting for buffalo. To help him, he hired an Indian Scout.
The two of them set off on their journey to find buffalo.

After riding awhile, the Indian gets off his horse, puts his ear to the ground and says "Humm, buffalo come".
The soldier scans the area with his binoculars, but sees nothing.

He is confused and says to the Indian, "I do not see anything, how do you know buffalo come?"

The Indian replies, "Ear sticky".