Search: beck and call
Why: At her bitchiest (she is always so mean to him because she thinks she's better than him - which she's not, BTW), Rachel tells Ross she wants him at her "constant beck and call."
Answer: According to Merriam-Webster:
A 'beck' is a silent signal, such as a nod of the head or a motion with the forefinger. The sense is apparent in the Earl of Worcester's Iulius Cesars Commentaryes (1470): 'It should be ready at a beck.' In summoning a servant one might have to resort to a 'call' as well as a 'beck' if the servant did not see the beck or failed to respond to it."Source: Phrases.org.uk
The More You Know: Other Becks: