To something is to slowly mix in a bit of with eggs or cream to raise the temperature slowly. This prevents the cream from curdling (turning lumpy and gross) or the eggs from scrambling in your sauce.

temper; hot sauce

Explanation:

The context clue here is "raise the temperature slowly" gives a quick clue to temper (as a verb). The 4th definition of temper (as a verb) is "to bring to a suitable state by mixing or adding a usually liquid ingredient." Knowning, this leads to the second blank being hot sauce, as that's a liquid.

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.