Stopper for a liquid dispensing opening

A stopper for a container, the container comprising a liquid dispensing opening and a main cavity, the liquid dispensing opening being smaller than the size of the main cavity, said stopper comprising a stem having a central axis and comprising a bottom limiter and a top limiter,

• said bottom limiter comprising an expandable arrangement being urged toward an expanded position in which it has a second diameter, greater than a first diameter being a reference diameter of the stopper, thereby preventing extraction of the stopper through the liquid dispensing opening in a first direction, and being configured for assuming, when a force is applied thereto in a second direction opposite said first direction, a retracted position in which it has a third diameter, no greater than the first diameter, facilitating its passage through said liquid dispensing opening,
• said top limiter having a fourth diameter greater than said first diameter, and being configured for maintaining said fourth diameter during use, thereby at least partially preventing displacement of the stopper through the liquid dispensing opening in said second direction,
• wherein said stopper is configured for allowing free passage of liquid through the liquid dispensing opening, at least between said stem and an inner surface of said liquid dispensing opening, and for blocking passage of particles of a predetermined size through the liquid dispensing opening.