Directly in front of [Father Wolf], holding on by a low branch, stood a naked brown baby who could just walk—as soft and as dimpled a little atom as ever came to a wolf's cave at night. (1.27)
We start the story from the animal's perspective, so an infant child in this environment is very foreign indeed.
"The others hate thee because their eyes cannot meet thine—because thou art wise—because thou hast pulled out thorns from their feet—because thou art a man." (1.88)
Even though Mowgli is raised by wolves, and he has always been kind and helpful to them, they fear him because he is different.
"What has a man to do with us? Let him go to his own place." (1.120)
Mowgli's "place" should be with his family—i.e. the wolves—but the other wolves believe that because he walks on two legs, he belongs with the rest of the men who walk on two legs.
The dawn was beginning to break when Mowgli went down the hillside alone, to meet those mysterious things that are called men. (1.146)
Although Mowgli is foreign to the wolves because he is a man, men are foreign to Mowgli, because he has no memory of living among them.
Mowgli was taught the Stranger's Hunting Call, which must be repeated aloud till it is answered, whenever one of the Jungle-People hunts outside his own grounds. (3.1)
Baloo teaches Mowgli to communicate with the creatures of the jungle to help him integrate better into this new-to-him social ecosystem.
"Except his own tribe," said Bagheera, under his breath. (3.19)
Baloo has taught Mowgli all the Master-Words so that he can communicate with any creature in the jungle… except for man. None of the animals in the jungle know how to communicate with man, probably because man is more likely to shoot first, ask questions never.
The priest came to the gate, and with him at least a hundred people, who stared and talked and shouted and pointed at Mowgli. (5.2)
Being a "wild boy," Mowgli is foreign to the men in the village, too. He just can't fit in anywhere, like a lonely little puzzle piece.
It was sorcery, magic of the worst kind, thought Buldeo, and he wondered whether the amulet round his neck would protect him. He lay as still as still, expecting every minute to see Mowgli turn into a tiger, too. (5.81)
Because Mowgli is wild and different, and seems to have a relationship with the animals, the villagers fear him. And because they fear him, they eventually decide to attack him.
"Only the holluschickie go to Otter Island. If we went there they would say we were afraid. We must preserve appearances, my dear." (7.13)
The seals are surprisingly stubborn; they won't go anywhere different even if it's less crowded and more comfortable. As Kotick will soon discover, they won't even relocate to save their own lives.
[The Viceroy of India] was receiving a visit from the Amir of Afghanistan—a wild king of a very wild country. (13.1)
We see a little bit of foreignness in the world of man, too. The soldiers of India think that the people of Afghanistan are weird and strange because they don't blindly follow the orders of their Amir, the way they follow the orders of their own leader.