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This is a common phenomenon and occurs mainly around storms.
These look like little "pouches" and are not little at all. Each is about 1km wide. They look like cells and, as such, as considered a cellular structure. These clouds appear around cumulonimbus storm clouds, and as they build up with water particles and the air around it cools, the cloud descends. At least, that is one version of why they descend. The other is that the ice crystals begin to melt, and the bottom of the cloud becomes heavy.
There is a factor that you can find in most weather apps like windy.app called the CAPE. Convective Available Potential Energy or CAPE is the amount of fuel available to a developing thunderstorm. This will also tell you when the mammatus cloud is likely to appear. CAPE is expressed in joules per kilogram (J/kg) and can range from zero to over 5000. In general, CAPE values of less than 1000J/kg represent weak instability, 1000 to 2500J/kg moderate instability, 2500-4000J/kg strong instability, and greater than 4000J/kg extreme instability. Instability usually occurs around low-pressure systems or troughs, ie where you see the word LOW (L) or a dashed line on a synoptic chart. Air flows towards a low-pressure system and then rises. Air flows clockwise around a low-pressure system in the Southern Hemisphere. Air flows down into a High-pressure system and then disperses. Air flows anti-clockwise around a high-pressure system in the Southern Hemisphere.
Monday's Riddle
What has no hands, no feet, no head, and no body, but can open any door?