Chewing the cud
Thinking about something/someone for a long time.
Person 1: Whatcha doing?
Person 2: Just chewing the cud.
Person 1: Ahhh I see bruv.
Person 2: Just chewing the cud.
Person 1: Ahhh I see bruv.
Chewing the cud
Giving oral sex to a lady for an especially prolonged period of time, and it not resulting in her having an orgasm.
"Ahhh yeah mate I was with Amelia last night and was chewing the cud for hours, my jaw aches"