When the American finds out that there is a snake under the table and tells everyone to not move or they will forfeit fifty rupees, none of the characters except the American that their is a snake underneath the table, The audience knows there is a snake under the table.
The little girl and the colonel are arguing if women are courageous or not. The argument contradicts with what the colonel says, when Mrs. Wynnes has a snake on top of her foot.
Your gender has no impact on how courageous you are. Mrs. Wynnes is a woman and she is courageous since she doesn't panic when a snake crawls over her foot.