The first trio is for the strings alone, with a theme that has a signature acciaccatura every few notes.
From the en.wikipedia.org
Exceptionally, the acciaccatura may be notated in the bar preceding the note to which it is attached, showing that it is to be played before the beat.
From the en.wikipedia.org
In some cases on instruments that permit it, such as the piano, the acciaccatura is sounded simultaneously with the principal note, and then immediately released.
From the en.wikipedia.org
More examples
Grace note: an embellishing note usually written in smaller size
In music, ornaments are musical flourishes that are not necessary to carry the overall line of the melody (or harmony), but serve instead to decorate or "ornament" that line. Many ornaments are performed as "fast notes" around a central note. ...
A short grace note (theoretically taking no time at all), occurring on the beat occupied by the main note to which it is prefixed, one scale-step higher or lower than that main note. ...
A note added before another as a decoration that 'theoretically' has no duration.
An Italian term for a very short note played immediately before the main note to which it is related
Musical adornment of the instruments of keyboard. It consists of the first note that happens quickly to another neighbor.