Answer from Dr. Locker
When a woman is sexually aroused, her vagina opens and is lubricated. This may make it seem wider than it had before arousal. Also, beyond the first third of the vagina, there is not a high concentration of nerve endings deep inside the vagina, so it is sometime difficult to feel what´s going on in there. To avoid saying "put it in" you can put it in yourself. If you are unsure if it´s in, use your hands to feel if it is, instead of telling him to put it in, or instead of asking, "Is it in yet."
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