It may be that it is winter, I do not know where you are, but in Michigan where I live the wild garter snakes are not active during the winter. It may be responding to the shorter days than in the summer.
IF you are afaid that it is something else, ask this question on the garter snake forum, or in the general snakes.
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0.0.1 Common Columbian Boa (Damian)
0.0.1 Amel Cornsnake (Kernal)
0.0.1 Okeetee Cornsnake (Guido)
1.1.0 Lhasa Apso's (Monkey, Tiffany)
1.0.0 Rat Terrier (Ricky)
1.3.0 Mice (nameless)
0.0.4 Goldfish (nameless)
0.1.0 Beta Fish (nameless)
0.0.1 Snail (Gary)"Meoow"
Also Canibal the Musical is just about the the most funny movie ever!!!