Now, a filibuster typically begins when a Senator or group of Senators signals their intent to filibuster – which can be done by a private conversation with the majority leader or by quietly placing a bill or nomination on hold. Given the modern Senate's scarce floor time, this threat is usually enough to table the disputed issue until the dissenting Senators cave or until there are definitely enough votes to invoke cloture.
2010 April 22, Mimi Murray Digby Marziani, Diana Lee, “Statement for the Record, Brennan Center for Justice, New York, NY”, in Examining the Filibuster: Hearings before the Committee on Rules and Administration, United States Senate, One Hundred Eleventh Congress, Second Session, April 22, 2010, May 19, 2010, June 23, 2010, July 28, 2010, and September 22 and 29, 2010 (S. Hrg. 111-706), Washington, D.C.: Government Printing Office, page 112