While the curve itself can shift, we also talk about shifts along the curve. This is our point going from one place on the curve to another place on the curve. For example, we might say the price shifted from 8 to 5. If it shifted along the curve, then the quantities would both be determined by the demand line.

import matplotlib.pyplot as plt
prices = []
hamburgers = []

for price in range(0,11):
    prices += [price]
    hamburgers += [15-price]
plt.plot(hamburgers,prices)
plt.plot(7,8, 'ro')
plt.plot(10,5, 'go')


plt.xlabel("Quantity Demanded")
plt.ylabel("Price")
plt.title("Prices Dropping")
ax = plt.axes()
ax.arrow(7.5, 8, 2.5, -2.5, head_width=0.2, head_length=0.1, fc='k', ec='k')
plt.show()

Nothing here is new, but the take away should be that if we are shifting along the curve, then as price goes up, our quantity has to go down.

Source Code