In a gradual manner:
— The snake moved gradually toward its victim.

synonyms: bit by bit, step by step.

Roget 26: by degrees, gradually, inasmuch, pro tanto [It]; however, howsoever; step by step, bit by bit, little by little, inch by inch, drop by drop; a little at a time, by inches, by slow degrees, by degrees, by little and little; in some degree, in some measure; to some extent; di grado in grado [Lat.].    ... show more

Roget 69: continuously etc. adj.; seriatim; in a line etc. n.; in succession, in turn; running, gradually, step by step, gradatim [Lat.], at a stretch; in file, in column, in single file, in Indian file.    ... show more

Roget 144: gradually, etc. (slowly) 275 in transitu etc. (transference) 270 [Lat.].   

Roget 275: slowly etc. adj.; leisurely; piano, adagio; largo, larghetto; at half speed, under easy sail; at a foots pace, at a snail's pace, at a funeral pace; in slow time, with mincing steps, with clipped wings; haud passibus aequis [Lat.] [Vergil]. gradually etc. adj.; gradatim [Lat.]; by degrees, by slow degrees, by inches, by little and little; step by step, one step at a time; inch by inch, bit by bit, little by little, seriatim; consecutively.    ... show more