I haven't traded stock indexes (SPX, NASDAQ-100, RUT, etc) or stock options in awhile. Can someone give me a quick refresher on how their implied vol curve and shapes (in general) behave? Is the curve or put skew (relative to the calls) likely to steepen (higher slope values between strikes) on a break vs a rally? Do vol curve skews flatten out in general for stocks on rallies? If the latter is the case, why does the CBOE SKEW indicator have such high readings when the stock market is on its highs and vol on its lows, and low readings when the VIX is 25+ and the market is in a panic sell-off? I also noticed that a few implied volatility skew indicators for the SPY had the puts exploding vs the calls during the last year's (late 2018) stock market meltdown, but yet at the same time the CBOE SKEW indicator was printing low values during this correction. I'm guessing that the SKEW indicator was no longer pricing in a fat tail event because it was already currently taking place in the markets, but that would imply that the put skew would also have flattened out if the downside fear was removed by the marketplace, which by all indications it did not, but rather steepened significantly vs the calls (higher strikes). And how often do you see the OTM call implied vols trading higher than the OTM puts for individual stocks? I can see this happening for takeover candidates, but which stocks in general have upside fear trumping the downside fear? Tech, Biotech, small cap? Or is this a rare occurrence and only seen during a low vol bull market environment.