the last 20 years had a bunch of research about various types of iconicity in spoken language. but even without knowing that! i speak*/hear languages! i can tell i/others do things that linguists used to say don't ever happen!
1900s generativists just... ignored a lot of stuff,, kinda, and that legacy stuck
so the books all like "signed languages do this thing! and no spoken language does anything like it!" meanwhile i can think of 3 example sentences in hebrew that do the exact thing...
israeli sign language: you can sign climbing a tree by one hand signing "tree", a sign that conveniently kinda looks like a tree, and having the other hand go up next to/on top of the other. when the story tells about coming back down, the hand that climbed up now goes back down
hebrew: if i'm telling a story about climbing a tree, i will increase my pitch to signify going up. when the story tells about coming back down, i'll decrease my pitch to signify going down