A cooling flush ensures the group head is clean, but also to control it's temperature. If you have ever noticed water sputtering from a group head along with excess steam? To eliminate this, a cooling flush can be utilised between shots. This is where an amount of water is flushed from the group head after you have removed the group handle and before the next espresso is extracted.
Texturing milk includes aerating the milk to its desired froth level before bringing it to the right temperature (60 to 65°C). As a simple rule, the more air you add to the milk, the more froth you build. In order to stretch the proteins, this needs to be done while the milk is cold - this helps build silky smooth foam.