같이

Like a..., as if it were

Attaches straight to a noun to compare something with it, and all eight lines here do exactly that: hard like a rock, looking like melted butter, absorbing like lotion, understanding perfectly, feeling like an idiot. 처럼 means the same thing and is interchangeable in most of these. Do not confuse it with the separate word 같이 meaning 'together', which is spelled and pronounced identically.