“See that?” he demanded.
Alec bent and scrutinised the blotter attentively. Just in front of Roger’s finger were a number of short lines not more than an inch or so long. The ones at the left-hand end were little more than scratches on the surface, not inked at all; those in the middle bore faint traces of ink; while towards the right end the ink was bold and the lines thick and decided. Beyond these were a few circular blots of ink. Apart from these markings, the sheet of white blotting paper, clearly fresh within the last day or two, had scarcely been used.
“Well?” said Roger triumphantly. “Make anything of it?”
“Nothing in particular,” Alec confessed, straightening up again. “I should say that somebody had been cleaning his pen on it.”
“In that case,” Roger returned with complacency, “it would become my painful duty to inform you that you were completely wrong.”
“Why? I don’t see it.”
“Then look again. If he had been cleaning his pen, Alexander Watson, the change from ink to the lack of it would surely be from left to right, wouldn’t it? Not from right to left?”
“Would it? He might have moved from right to left.”
“It isn’t natural. Besides, look at these little strokes. Nearly all of them have a slight curve in the tail towards the right. That means they must have been made from left to right. Guess again.”
“Oh, well, let’s try the reverse,” said Alec, nettled into irony. “He wasn’t cleaning his pen at all; he was dirtying it.”