The frogs whistle is when you are about to ejaculate from oral sex, you grab the back your partner's head and force it on your cock as you cum, while you squeeze their nipples without telling them. Their scream and the cum gargling in their thought will make out the sound of a frog whistling
Guy getting head: boutta cum bitch
Bitch: oka-jfghghhththththtthththtth
Guy getting head: fuck yea frog whistle you whore
Frogs whistle