On a shakeout, the supply vacuum has already happened, and if...

On a shakeout, the supply vacuum has already happened, and if you had been watching a smaller time frame, it would have been clear.
For instance, if it was a 'daily' shakeout, and it went down in the morning, and back up in the afternoon, if you were watching a 3hr chart for instance, it would be a shakeout over two bars (two bar reversal) instead of one.
Here is what has happened - price has rammed down violently, and all the stock has secretly been absorbed, and stops may have been triggered and bought.
Then, because there is no further selling pressure at this level (because all the sellers have been absorbed or their supply has been bought), price then floats up easily (within the supply vacuum) and eventually closes back near the highs again.
So any shakeout, on any timeframe, if looked at on a smaller timeframe, will see this principle.
This is seen fairly regularly across the market, and price will often continue higher after this is seen (because shakeouts are a sign of potential strength), but the actual 'supply vacuum' is temporary, and is over fairly quickly in most cases.
(Steve Phillips often traded the news, on US Indicies and various currencies, using this 'supply vacuum' principle)

They also come in different sizes (from massively big, to little mini ones), and big ones are where there is a really serious climactic action bar on massive volume.....like a selling climax.
When this happens, a really large and widespread supply vacuum may be formed, which may last a few bars when it recovers.
This is the Automatic Rally or Automatic Reaction (AR) which Wyckoff spoke of.
This type of rally will often also show where the supply is sitting above, and also mark where the 'creek' is.
(mind you if this happened on a daily timeframe, then looking at the weekly chart, it might just look like a single bar shakeout, so it is all relative to the time frame you are working in)

cheers