Suggestion:
This type of glyph is showing twins, indicated by two heads on the same body.
Its appearance among the glyphs for Thursday affirms this reading. For Thursday is a
day of thunder and lightning according to folklore all over the world. And the thunder is connected with a pair of twins.
The logic behind these ideas is that thunder and lightning means
rain. And rain means fertility. And twins is a sign of fertility.
Reference: Harris