A chart tells thousand words. The pair completed a pullback to the longer-term trendline and formed a fresh lower low on the daily chart. Some traders may find this enough to enter with a short position, but I like to have some additional confirmation. A lower low doesn't necessarily mean a lower high, since the price can still go to the upside and create a higher high instead. That's why I would like for a non-failure swing, which would be a new lower high as shown on the chart. A short trigger would be the break below the recent lower low (shown on chart). Notice that a fresh lower high would imply a head and shoulders pattern.