My impression is that the presence or absence, as the case might be, of a divergent squint would be accepted as absolute disproof of identity.

But here we are." He inserted the key into the wicket of the large gate, and, when we had stepped through into the covered way, he locked it from the inside.
"Why have you locked us in ?" I asked, seeing that the wicket had a latch.
"Because," he replied, "if we now hear any one on the premises we shall know who it is.

Only one person besides ourselves has a key." His reply startled me somewhat.

I stopped and looked at him.
"That is a quaint situation, Thorndyke.

I hadn't thought of it.