Mikvaot, Chapter Ten, Mishnah Four
Today’s mishnah is the opposite of yesterday’s. It deals with situations in which water does need to come into contact with the insides of knots or other such cases.
The following require that water shall enter inside them:
1) The knot in an undergarment which is tied to the shoulder.
2) The hem of a sheet must be stretched out.
3) And the knot of head tefillin if it is not fastened tightly,
4) Or of the arm-tefillin if it moves up and down.
5) And the laces of a sandal.
6) Clothes which are immersed when they have just been washed must be kept immersed until they bubble up;
a) But if they are immersed when already dry, they must be kept immersed until they throw up bubbles and then cease to bubble up.
Section one: The undergarment was attached to the shoulders by a knot. Since this knot would regularly be undone, it needs to allow water inside when immersed.
Section two: Before one immerses the hem of a sheet which has wrinkles and folds in it, one must stretch it out so that the water comes into contact with every part.
Sections three and four: These were explained in yesterday’s mishnah.
Section five: While the thong of a sandal did not need to let the water inside it, the laces are regularly undone. Therefore, they need to be undone to allow water in and out.
Section six: The mishnah requires a sign that the water has come into contact with the clothes for the immersion to be efective. If the clothes are already wet, then all that needs to happen is for the clothes to sort of bubble up, meaning they pop up to the surface.
If they are already dry, then the clothes must first bubble up and then stop bubbling up to the surface. Only this is a sign that they have been successfully immersed.