Oops. This is supposed to read ve-sar me-hem, but some sort of lapse in concentration has caused the scribe to miss out the "me" and cut straight to the "hem," realising that something was wrong partway through the hey.
A bit of blotting paper is used to take up as much of the wet ink as possible. One doesn't have to do this, but it makes it easier later. Unlike marker pens, Torah ink sits on top of the parchment, and doesn't soak all the way through, so it can be scraped off quite easily. It's very like a kitchen spill - scraping off a lot of yuk once it's dried is hard work and messy, and it's much easier to mop up as much as you can while it's still wet.
Some scribes make two little marks in pencil, one above the mistake and one in the margin, so they'll know where to come back to when the ink is dry. Without some sort of marker, finding mistakes later is a bit like Where's Wally but not knowing how many Wallys you're supposed to find. It's a real pain and you might miss one, which would be bad since even one mistake technically invalidates the whole Torah. Not all scribes do this. Presumably the scribes who don't are really, really good at Where's Wally.
Erasing tools. From left to right: electric eraser, #10 surgical scalpel, bone folder, rose thorns, plastic eraser.
Once the mistake is dry, the remaining ink is scraped off. The electric eraser has a specially abrasive type of eraser in it, which makes quick work of the job (see below). For tiny mistakes, or delicate areas where the electric won't fit, one can use a surgical scalpel with a good sharp blade (see right). You may have heard that one can't use metal tools on a Torah, because ordinary metals have associations with war and hurting people. But surgical scalpels are used to save lives, not take them, so that makes a difference. Other scribes use gold knives or glass shards, for the same reason.
Once the mistake is dry, the remaining ink is scraped off. The electric eraser has a specially abrasive type of eraser in it, which makes quick work of the job (see below). For tiny mistakes, or delicate areas where the electric won't fit, one can use a surgical scalpel with a good sharp blade (see right). You may have heard that one can't use metal tools on a Torah, because ordinary metals have associations with war and hurting people. But surgical scalpels are used to save lives, not take them, so that makes a difference. Other scribes use gold knives or glass shards, for the same reason.
The surface is usually a bit ruffled after this, which makes it hard to write on, so it is smoothed and burnished with a bone folder or other burnishing tool. If the surface is very bad, powdered gum sanderac may be added, which stops the ink misbehaving. Then the guideline is marked back in. An awl is a sensible tool for this, but a rose thorn is a traditional non-metal alternative. Both are sharp enough to mark the surface without being so sharp they will cut through it.
Finally, the proper letter is written in, always by copying it from a tikkun. Here the ink is still wet, so the new letters are more shiny than the old ones.
One does not use correction fluid.