Weird thing on my tree?

Question

Yeah Well I walked out of my house this morning and I noticed this weird thing on my tree. It's this weird bubble thing. It looked like a really ginormous zit. So I got a stick from the ground and popped it. This green yellowish stuff oozed out on the ground. so then I went back to look at it later this afternoon and another zit thingy is growing back on. It's so weird. Does anyone know what this is or might be?

Answer 1

Pitch or sap.  When a tree is wounded by an insect or attacked by fungus it oozes pitch out to expel the foreign body.  Its like us bleeding.  When it does this it shows the tree is healthy.  When it is injured and doesn't ooze it is unhealthy, just like we would be if we didn't bleed if stabbed.

Answer 2

Sap.