Brace to brassiere and shouter to shunter

Braces were commonly worn by men to hold their trousers up at this time, so we've got Juan and Issy in shirtsleeves, his braces touching her bra because they are working shoulder to shoulder. The image I get here is of Juan wanting to do hard work with Issy that explains their being partially undressed and covers the thrill he's getting from being close to her in that way.