I have semantic chaos in my head. 'Crawl', 'crouch', 'creep', 'cower' — those words come to my head when I'm thinking about a hunting, say, tiger. Often, when I need to express some meaning, a whole thesaurus (or something that feels like one) pops up in my mind instead of one specific and accurate word that I'm seeking. The problem is the words constituting such a thesaurus are melted together into a shapeless ugly clump in my head and it's difficult for me to separate them from one another. I can look them up in dictionaries but: 1) the knowledge doesn't last long, unfortunately; 2) often, dictionaries don't do a good job spelling out semantic and usage differences between words with similar meanings. "How can I fix this problem?" — this is your additional question you may not answer. The main question, in line with the title, is what should I write in place of the blanks.
The tiger slowly approached the gazelle, ____ing, ready to attack at any moment.
The tiger (slowly) _____ed to the gazelle, ready to attack at any moment.