rs3749977, also known as Arg226Gln, is a SNP in the olfactory receptor OR2J3 gene. The rarer allele is apparently always found with the rarer allele of rs28757581, according to [R].
A study of 52 unrelated volunteers who were not anosmic tested their ability to detect cis-3-hexen-1-ol (C3HEX), a compound given off by "wounded" plants, most typically, cut grass. The rarer alleles of rs3749977 and rs28757581 were associated with a lowered ability to detect this smell.[R]