To sign glass, take your dominant hand's bent index finger and tap it against one of your front teeth as your mouth is slightly open and exposing your pearly whites.
Teach your toddler the glass sign when they are old enough to graduate from drinking their water, milk, or juice from their baby bottle or sippy cup. You could also start teaching them the glass sign as soon as they ask you why you and the older siblings use a drinking glass, while your toddler still uses their plastic bottle.
Teach your toddler this sign in contrast with the other drinking containers they have gotten used to, and eventually along with the many eating and cooking implements flash cards as well.
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